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✏️ Editing: FAQ.txt

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 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
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IMAP Toolkit Frequently Asked Questions

Table of Contents

* 1. General/Software Feature Questions
          + 1.1 Can I set up a POP or IMAP server on UNIX/Linux/OSF/etc.?
          + 1.2 I am currently using qpopper as my POP3 server on UNIX.
            Do I need to replace it with ipop3d in order to run imapd?
          + 1.3 Can I set up a POP or IMAP server on Windows XP, 2000,
            NT, Me, 98, or 95?
          + 1.4 Can I set up a POP or IMAP server on Windows 3.1 or DOS?
          + 1.5 Can I set up a POP or IMAP server on Macintosh?
          + 1.6 Can I set up a POP or IMAP server on VAX/VMS?
          + 1.7 Can I set up a POP or IMAP server on TOPS-20?
          + 1.8 Are hierarchical mailboxes supported?
          + 1.9 Are "dual-use" mailboxes supported?
          + 1.10 Can I have a mailbox that has both messages and
            sub-mailboxes?
          + 1.11 What is the difference between "mailbox" and "folder"?
          + 1.12 What is the status of internationalization?
          + 1.13 Can I use SSL?
          + 1.14 Can I use TLS and the STARTTLS facility?
          + 1.15 Can I use CRAM-MD5 authentication?
          + 1.16 Can I use APOP authentication?
          + 1.17 Can I use Kerberos V5?
          + 1.18 Can I use PAM for plaintext passwords?
          + 1.19 Can I use Kerberos 5 for plaintext passwords?
          + 1.20 Can I use AFS for plaintext passwords?
          + 1.21 Can I use DCE for plaintext passwords?
          + 1.22 Can I use the CRAM-MD5 database for plaintext passwords?
          + 1.23 Can I disable plaintext passwords?
          + 1.24 Can I disable plaintext passwords on unencrypted
            sessions, but allow them on encrypted sessions?
          + 1.25 Can I use virtual hosts?
          + 1.26 Can I use RPOP authentication?
          + 1.27 Can I use Kerberos V4?
          + 1.28 Is there support for S/Key or OTP?
          + 1.29 Is there support for NTLM or SPA?
          + 1.30 Is there support for mh?
          + 1.31 Is there support for qmail and the maildir format?
          + 1.32 Is there support for the Cyrus mailbox format?
          + 1.33 Is this software Y2K compliant?
     * 2. What Do I Need to Build This Software?
          + 2.1 What do I need to build this software with SSL on UNIX?
          + 2.2 What do I need to build this software with Kerberos V on
            UNIX?
          + 2.3 What do I need to use a C++ compiler with this software
            to build my own application?
          + 2.4 What do I need to build this software on Windows?
          + 2.5 What do I need to build this software on DOS?
          + 2.6 Can't I use Borland C to build this software on the PC?
          + 2.7 What do I need to build this software on the Mac?
          + 2.8 What do I need to build this software on VMS?
          + 2.9 What do I need to build this software on TOPS-20?
          + 2.10 What do I need to build this software on Amiga or OS/2?
          + 2.11 What do I need to build this software on Windows CE?
     * 3. Build and Configuration Questions
          + 3.1 How do I configure the IMAP and POP servers on UNIX?
          + 3.2 I built and installed the servers according to the BUILD
            instructions. It can't be that easy. Don't I need to write a
            config file?
          + 3.3 How do I make the IMAP and POP servers look for INBOX at
            some place other than the mail spool directory?
          + 3.4 How do I make the IMAP server look for secondary folders
            at some place other than the user's home directory?
          + 3.5 How do I configure SSL?
          + 3.6 How do I configure TLS and the STARTTLS facility?
          + 3.7 How do I build/install OpenSSL and obtain/create
            certificates for use with SSL?
          + 3.8 How do I configure CRAM-MD5 authentication?
          + 3.9 How do I configure APOP authentication?
          + 3.10 How do I configure Kerberos V5?
          + 3.11 How do I configure PAM for plaintext passwords?
          + 3.12 It looks like all I have to do to make the server use
            Kerberos is to build with PAM on my Linux system, and set it
            up in PAM for Kerberos passwords. Right?
          + 3.13 How do I configure Kerberos 5 for plaintext passwords?
          + 3.14 How do I configure AFS for plaintext passwords?
          + 3.15 How do I configure DCE for plaintext passwords?
          + 3.16 How do I configure the CRAM-MD5 database for plaintext
            passwords?
          + 3.17 How do I disable plaintext passwords?
          + 3.18 How do I disable plaintext passwords on unencrypted
            sessions, but allow them in SSL or TLS sessions?
          + 3.19 How do I configure virtual hosts?
          + 3.20 Why do I get compiler warning messages such as:
               o passing arg 3 of `scandir' from incompatible pointer
                 type
               o Pointers are not assignment-compatible.
               o Argument #4 is not the correct type.
            during the build?
          + 3.21 Why do I get compiler warning messages such as
               o Operation between types "void(*)(int)" and "void*" is
                 not allowed.
               o Function argument assignment between types "void*" and
                 "void(*)(int)" is not allowed.
               o Pointers are not assignment-compatible.
               o Argument #5 is not the correct type.
            during the build?
          + 3.22 Why do I get linker warning messages such as:
               o mtest.c:515: the `gets' function is dangerous and should
                 not be used.
            during the build? Isn't this a security bug?
          + 3.23 Why do I get linker warning messages such as:
               o auth_ssl.c:92: the `tmpnam' function is dangerous and
                 should not be used.
            during the build? Isn't this a security bug?
          + 3.24 OK, suppose I see a warning message about a function
            being "dangerous and should not be used" for something other
            than this gets() or tmpnam() call?
     * 4. Operational Questions
          + 4.1 How can I enable anonymous IMAP logins?
          + 4.2 How do I set up an alert message that each IMAP user will
            see?
          + 4.3 How does the c-client library choose which of its several
            mechanisms to use to establish an IMAP connection to the
            server? I noticed that it can connect on port 143, port 993,
            via rsh, and via ssh.
          + 4.4 I am using a TLS-capable IMAP server, so I don't need to
            use /ssl to get encryption. However, I want to be certain
            that my session is TLS encrypted before I send my password.
            How to I do this?
          + 4.5 How do I use one of the alternative formats described in
            the formats.txt document? In particular, I hear that mbx
            format will give me better performance and allow shared
            access.
          + 4.6 How do I set up shared mailboxes?
          + 4.7 How can I make the server syslogs go to someplace other
            than the mail syslog?
     * 5. Security Questions
          + 5.1 I see that the IMAP server allows access to arbitary
            files on the system, including /etc/passwd! How do I disable
            this?
          + 5.2 I've heard that IMAP servers are insecure. Is this true?
          + 5.3 How do I know that I have the most secure version of the
            server?
          + 5.4 I see all these strcpy() and sprintf() calls, those are
            unsafe, aren't they?
          + 5.5 Those /tmp lock files are protected 666, is that really
            right?
     * 6. Why Did You Do This Strange Thing? Questions
          + 6.1 Why don't you use GNU autoconfig / automake /
            autoblurdybloop?
          + 6.2 Why do you insist upon a build with -g? Doesn't it waste
            disk and memory space?
          + 6.3 Why don't you make c-client a shared library?
          + 6.4 Why don't you use iconv() for internationalization
            support?
          + 6.5 Why is the IMAP server connected to the home directory by
            default?
          + 6.6 I have a Windows system. Why isn't the server plug and
            play for me?
          + 6.7 I looked at the UNIX SSL code and saw that you have the
            SSL data payload size set to 8192 bytes. SSL allows 16K; why
            aren't you using the full size?
          + 6.8 Why is an mh format INBOX called #mhinbox instead of just
            INBOX?
          + 6.9 Why don't you support the maildir format?
          + 6.10 Why don't you support the Cyrus format?
          + 6.11 Why is it creating extra forks on my SVR4 system?
          + 6.12 Why are you so fussy about the date/time format in the
            internal "From " line in traditional UNIX mailbox files? My
            other mail program just considers every line that starts with
            "From " to be the start of the message.
          + 6.13 Why is traditional UNIX format the default format?
          + 6.14 Why do you write this "DON'T DELETE THIS MESSAGE --
            FOLDER INTERNAL DATA" message at the start of traditional
            UNIX and MMDF format mailboxes?
          + 6.15 Why don't you stash the mailbox metadata in the first
            real message of the mailbox instead of writing this fake
            FOLDER INTERNAL DATA message?
          + 6.16 Why aren't "dual-use" mailboxes the default?
          + 6.17 Why do you use ucbcc to build on Solaris?
          + 6.18 Why should I care about some old system with BSD
            libraries? cc is the right thing on my Solaris system!
          + 6.19 Why do you insist upon writing .lock files in the spool
            directory?
          + 6.20 Why should I care about compatibility with the past?
     * 7. Problems and Annoyances
          + 7.1 Help! My INBOX is empty! What happened to my messages?
          + 7.2 Help! All my messages in a non-INBOX mailbox have been
            concatenated into one message which claims to be from me and
            has a subject of the file name of the mailbox! What's going
            on?
          + 7.3 Why do I get the message:
               o CREATE failed: Can't create mailbox node xxxxxxxxx: File
                 exists
            and how do I fix it?
          + 7.4 Why can't I log in to the server? The user name and
            password are right!
          + 7.5 Help! My load average is soaring and I see hundreds of
            POP and IMAP servers, many logged in as the same user!
          + 7.6 Why does mail disappear even though I set "keep mail on
            server"?
          + 7.7 Why do I get the message
               o Moved ##### bytes of new mail to /home/user/mbox from
                 /var/spool/mail/user
            and why did this happen?
          + 7.8 Why isn't it showing the local host name as a
            fully-qualified domain name?
          + 7.9 Why is the local host name in the From/Sender/Message-ID
            headers of outgoing mail not coming out as a fully-qualified
            domain name?
          + 7.10 What does the message:
               o Mailbox vulnerable - directory /var/spool/mail must have
                 1777 protection
            mean? How can I fix this?
          + 7.11 What does the message:
               o Mailbox is open by another process, access is readonly
            mean? How do I fix this?
          + 7.12 What does the message:
               o Can't get write access to mailbox, access is readonly
            mean?
          + 7.13 I set my POP3 client to "delete messages from server"
            but they never get deleted. What is wrong?
          + 7.14 What do messages such as:
               o Message ... UID ... already has UID ...
               o Message ... UID ... less than ...
               o Message ... UID ... greater than last ...
               o Invalid UID ... in message ..., rebuilding UIDs
            mean?
          + 7.15 What do the error messages:
               o Unable to read internal header at ...
               o Unable to find CRLF at ...
               o Unable to parse internal header at ...
               o Unable to parse message date at ...
               o Unable to parse message flags at ...
               o Unable to parse message UID at ...
               o Unable to parse message size at ...
               o Last message (at ... ) runs past end of file ...
            mean? I am using mbx format.
          + 7.16 What do the syslog messages:
               o imap/tcp server failing (looping)
               o pop3/tcp server failing (looping)
            mean? When it happens, the listed service shuts down. How can
            I fix this?
          + 7.17 What does the syslog message:
               o Mailbox lock file /tmp/.600.1df3 open failure:
                 Permission denied
            mean?
          + 7.18 What do the syslog messages:
               o Command stream end of file, while reading line user=...
                 host=...
               o Command stream end of file, while reading char user=...
                 host=...
               o Command stream end of file, while writing text user=...
                 host=...
            mean?
          + 7.19 Why did my POP or IMAP session suddenly disconnect? The
            syslog has the message:
               o Killed (lost mailbox lock) user=... host=...
          + 7.20 Why does my IMAP client show all the files on the
            system, recursively from the UNIX root directory?
          + 7.21 Why does my IMAP client show all of my files,
            recursively from my UNIX home directory?
          + 7.22 Why does my IMAP client show that I have mailboxes named
            "#mhinbox", "#mh", "#shared", "#ftp", "#news", and "#public"?
          + 7.23 Why does my IMAP client show all my files in my home
            directory?
          + 7.24 Why is there a long delay before I get connected to the
            IMAP or POP server, no matter what client I use?
          + 7.25 Why is there a long delay in Pine or any other c-client
            based application call before I get connected to the IMAP
            server? The hang seems to be in the c-client mail_open()
            call. I don't have this problem with any other IMAP client.
            There is no delay connecting to a POP3 or NNTP server with
            mail_open().
          + 7.26 Why does a message sometimes get split into two or more
            messages on my SUN system?
          + 7.27 Why did my POP or IMAP session suddenly disconnect? The
            syslog has the message:
               o Autologout user=<...my user name...> host=<...my imap
                 server...>
          + 7.28 What does the UNIX error message:
               o TLS/SSL failure: myserver: SSL negotiation failed
            mean?
          + 7.29 What does the PC error message:
               o TLS/SSL failure: myserver: Unexpected TCP input
                 disconnect
            mean?
          + 7.30 What does the error message:
               o TLS/SSL failure: myserver: Server name does not match
                 certificate
            mean?
          + 7.31 What does the UNIX error message:
               o TLS/SSL failure: myserver: self-signed certificate
            mean?
          + 7.32 What does the PC error message
               o TLS/SSL failure: myserver: Self-signed certificate or
                 untrusted authority
            mean?
          + 7.33 What does the UNIX error message:
               o TLS/SSL failure: myserver: unable to get local issuer
                 certificate
            mean?
          + 7.34 Why does reading certain messages hang when using
            Netscape? It works fine with Pine!
          + 7.35 Why does Netscape say that there's a problem with the
            IMAP server and that I should "Contact your mail server
            administrator."?
          + 7.36 Why is one user creating huge numbers of IMAP or POP
            server sessions?
          + 7.37 Why don't I get any new mail notifications from Outlook
            Express or Outlook after a while?
          + 7.38 Why don't I get any new mail notifications from
            Entourage?
          + 7.39 Why doesn't Entourage work at all?
          + 7.40 Why doesn't Netscape Notify (NSNOTIFY.EXE) work at all?
          + 7.41 Why can't I connect via SSL to Eudora? It says the
            connection has been broken, and in the server syslogs I see
            "Command stream end of file".
          + 7.42 Sheesh. Aren't there any good IMAP clients out there?
          + 7.43 But wait! PC Pine (or other PC program build with
            c-client) crashes with the message
               o incomplete SecBuffer exceeds maximum buffer size
            when I use SSL connections. This is a bug in c-client, right?
          + 7.44 My qpopper users keep on getting the DON'T DELETE THIS
            MESSAGE -- FOLDER INTERNAL DATA if they also use Pine or
            IMAP. How can I fix this?
          + 7.45 Help! I installed the servers but I can't connect to
            them from my client!
          + 7.46 Why do I get the message
               o Can not authenticate to SMTP server: 421 SMTP connection
                 went away!
            and why did this happen? There was also something about
               o SECURITY PROBLEM: insecure server advertised AUTH=PLAIN
          + 7.47 Why do I get the message
               o SMTP Authentication cancelled
            and why did this happen? There was also something about
               o SECURITY PROBLEM: insecure server advertised AUTH=PLAIN
          + 7.48 Why do I get the message
               o Invalid base64 string
            when I try to authenticate to a Cyrus server?
     * 8. Where to Go For Additional Information
          + 8.1 Where can I go to ask questions?
          + 8.2 I have some ideas for enhancements to IMAP. Where should
            I go?
          + 8.3 Where can I read more about IMAP and other email
            protocols?
          + 8.4 Where can I find out more about setting up and
            administering an IMAP server?
     _________________________________________________________________

1. General/Software Feature Questions
     _________________________________________________________________

1.1 Can I set up a POP or IMAP server on UNIX/Linux/OSF/etc.?

Yes. Refer to the UNIX specific notes in files CONFIG and
          BUILD.
     _________________________________________________________________

1.2 I am currently using qpopper as my POP3 server on UNIX. Do I need
   to replace it with ipop3d in order to run imapd?

Not necessarily.

Although ipop3d interoperates with imapd better than qpopper,
          imapd and qpopper will work together. The few qpopper/imapd
          interoperability issues mostly affect users who use both IMAP
          and POP3 clients; those users would probably be better served
          if their POP3 server is ipop3d.

If you are happy with qpopper and just want to add imapd, you
          should do that, and defer a decision on changing qpopper to
          ipop3d. That way, you can get comfortable with imapd's
          performance, without changing anything for your qpopper users.

Many sites have subsequently decided to change from qpopper to
          ipop3d in order to get better POP3/IMAP interoperability. If
          you need to do this, you'll know. There also seems to be a way
          to make qpopper work better with imapd; see the answer to the
          My qpopper users keep on getting the DON'T DELETE THIS MESSAGE
          -- FOLDER INTERNAL DATA if they also use Pine or IMAP. How can
          I fix this? question.
     _________________________________________________________________

1.3 Can I set up a POP or IMAP server on Windows XP, 2000, NT, Me, 98,
   or 95?

Yes. Refer to the NT specific notes in files CONFIG and BUILD.
          Also, for DOS-based versions of Windows (Windows Me, 98, and
          95) you *must* set up CRAM-MD5 authentication, as described in
          md5.txt.

There is no file access control on Windows 9x or Me, so you
          probably will have to do modifications to env_unix.c to prevent
          people from hacking others' mail.

Note, however, that the server is not plug and play the way it
          is for UNIX.
     _________________________________________________________________

1.4 Can I set up a POP or IMAP server on Windows 3.1 or DOS?
   1.5 Can I set up a POP or IMAP server on Macintosh?
   1.6 Can I set up a POP or IMAP server on VAX/VMS?

Yes, it's just a small matter of programming.
     _________________________________________________________________

1.7 Can I set up a POP or IMAP server on TOPS-20?

You have a TOPS-20 system? Cool.

If IMAP2 (RFC 1176) is good enough for you, you can use MAPSER
          which is about the ultimate gonzo pure TOPS-20 extended
          addressing assembly language program. Unfortunately, IMAP2 is
          barely good enough for Pine these days, and most other IMAP
          clients won't work with IMAP2 at all. Maybe someone will hack
          MAPSER to do IMAP4rev1 some day.

We don't know if anyone wrote a POP3 server for TOPS-20. There
          definitely was a POP2 server once upon a time.

Or you can port the POP and IMAP server from this IMAP toolkit
          to it. All that you need for a first stab is to port the MTX
          driver. That'll probably be just a couple of hours of hacking.
     _________________________________________________________________

1.8 Are hierarchical mailboxes supported?
   1.9 Are "dual-use" mailboxes supported?
   1.10 Can I have a mailbox that has both messages and sub-mailboxes?

Yes. However, there is one important caveat.

Some mailbox formats, including the default which is the
          traditional UNIX mailbox format, are stored as a single file
          containing all the messages. UNIX does not permit a name in the
          filesystem to be both a file and a directory; consequently you
          can not have a sub-mailbox within a mailbox that is in one of
          these formats.

This is not a limitation of the software; this is a limitation
          of UNIX. For example, there are mailbox formats in which the
          name is a directory and each message is a file within that
          directory; these formats support sub-mailboxes within such
          mailboxes. However, for technical reasons, the "flat file"
          formats are generally preferred since they perform better. Read
          imap-2007/docs/formats.txt for more information on this topic.

It is always permissible to create a directory that is not a
          mailbox, and have sub-mailboxes under it. The easiest way to
          create a directory is to create a new mailbox inside a
          directory that doesn't already exist. For example, if you
          create "Mail/testbox" on UNIX, the directory "Mail/" will
          automatically be created and then the mailbox "testbox" will be
          created as a sub-mailbox of "Mail/".

It is also possible to create the name "Mail/" directly. Check
          the documentation for your client software to see how to do
          this with that software.

Of course, on Windows systems you would use "\" instead of "/".
     _________________________________________________________________

1.11 What is the difference between "mailbox" and "folder"?

The term "mailbox" is IMAP-speak for what a lot of software
          calls a "folder" or a "mail folder". However, "folder" is often
          used in other contexts to refer to a directory, for example, in
          the graphic user interface on both Windows and Macintosh.

A "mailbox" is specifically defined as a named object that
          contains messages. It is not required to be capable of
          containing other types of objects including other mailboxes;
          although some mailbox formats will permit this.

In IMAP-speak, a mailbox which can not contain other mailboxes
          is called a "no-inferiors mailbox". Similarly, a directory
          which can not contain messages is not a mailbox and is called a
          "no-select name".
     _________________________________________________________________

1.12 What is the status of internationalization?

The IMAP toolkit is partially internationalized and
          multilingualized.

Searching is supported in the following charsets: US-ASCII,
          UTF-8, ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4,
          ISO-8859-5, ISO-8859-6, ISO-8859-7, ISO-8859-8, ISO-8859-9,
          ISO-8859-10, ISO-8859-11, ISO-8859-13, ISO-8859-14,
          ISO-8859-15, ISO-8859-16, KOI8-R, KOI8-U (alias KOI8-RU),
          TIS-620, VISCII, ISO-2022-JP, ISO-2022-KR, ISO-2022-CN,
          ISO-2022-JP-1, ISO-2022-JP-2, GB2312 (alias CN-GB),
          CN-GB-12345, BIG5 (alias CN-BIG5), EUC-JP, EUC-KR, Shift_JIS,
          Shift-JIS, KS_C_5601-1987, KS_C_5601-1992, WINDOWS_874,
          WINDOWS-1250, WINDOWS-1251, WINDOWS-1252, WINDOWS-1253,
          WINDOWS-1254, WINDOWS-1255, WINDOWS-1256, WINDOWS-1257,
          WINDOWS-1258.

All ISO-2022-?? charsets are treated identically, and support
          ASCII, JIS Roman, hankaku katakana, ISO-8859-[1 - 10], TIS, GB
          2312, JIS X 0208, JIS X 0212, KSC 5601, and planes 1 and 2 of
          CNS 11643.

EUC-JP includes support for JIS X 0212 and hankaku katakana.

c-client library support also exists to convert text in any of
          the above charsets into Unicode, including headers with MIME
          encoded-words.

There is no support for localization (e.g. non-English error
          messages) at the present time, but such support is planned.
     _________________________________________________________________

1.13 Can I use SSL?

Yes. See the answer to the How do I configure SSL? question.
     _________________________________________________________________

1.14 Can I use TLS and the STARTTLS facility?

Yes. See the answer to the How do I configure TLS and the
          STARTTLS facility? question.
     _________________________________________________________________

1.15 Can I use CRAM-MD5 authentication?

Yes. See the answer to the How do I configure CRAM-MD5
          authentication? question.
     _________________________________________________________________

1.16 Can I use APOP authentication?

Yes. See the How do I configure APOP authentication? question.

Note that there is no client support for APOP authentication.
     _________________________________________________________________

1.17 Can I use Kerberos V5?

Yes. See the answer to the How do I configure Kerberos V5?
          question.
     _________________________________________________________________

1.18 Can I use PAM for plaintext passwords?

Yes. See the answer to the How do I configure PAM for plaintext
          passwords? question.
     _________________________________________________________________

1.19 Can I use Kerberos 5 for plaintext passwords?

Yes. See the answer to the How do I configure Kerberos 5 for
          plaintext passwords? question.
     _________________________________________________________________

1.20 Can I use AFS for plaintext passwords?

Yes. See the answer to the How do I configure AFS for plaintext
          passwords? question.
     _________________________________________________________________

1.21 Can I use DCE for plaintext passwords?

Yes. See the answer to the How do I configure DCE for plaintext
          passwords? question.
     _________________________________________________________________

1.22 Can I use the CRAM-MD5 database for plaintext passwords?

Yes. See the answer to the How do I configure the CRAM-MD5
          database for plaintext passwords? question.
     _________________________________________________________________

1.23 Can I disable plaintext passwords?

Yes. See the answer to the How do I disable plaintext
          passwords? question.
     _________________________________________________________________

1.24 Can I disable plaintext passwords on unencrypted sessions, but
   allow them on encrypted sessions?

Yes. See the answer to the How do I disable plaintext passwords
          on unencrypted sessions, but allow them in SSL or TLS sessions?
          question.
     _________________________________________________________________

1.25 Can I use virtual hosts?

Yes. See the answer to the How do I configure virtual hosts?
          question.
     _________________________________________________________________

1.26 Can I use RPOP authentication?

There is no support for RPOP authentication.
     _________________________________________________________________

1.27 Can I use Kerberos V4?

Kerberos V4 is not supported. Kerberos V4 client-only
          contributed code is available in

ftp://ftp.cac.washington.edu/mail/kerberos4-patches.tar.Z

This is a patchkit which must be applied to the IMAP toolkit
          according to the instructions in the patchkit's README. We can
          not promise that this code works.
     _________________________________________________________________

1.28 Is there support for S/Key or OTP?

There is currently no support for S/Key or OTP. There may be an
          OTP SASL authenticator available from third parties.
     _________________________________________________________________

1.29 Is there support for NTLM or SPA?

There is currently no support for NTLM or SPA, nor are there
          any plans to add such support. In general, I avoid
          vendor-specific mechanisms. I also believe that these
          mechanisms are being deprecated by their vendor.

There may be an NTLM SASL authenticator available from third
          parties.
     _________________________________________________________________

1.30 Is there support for mh?

Yes, but only as a legacy format. Your mh format INBOX is
          accessed by the name "#mhinbox", and all other mh format
          mailboxes are accessed by prefixing "#mh/" to the name, e.g.
          "#mh/foo". The mh support uses the "Path:" entry in your
          .mh_profile file to identify the root directory of your mh
          format mailboxes.

Non-legacy use of mh format is not encouraged. There is no
          support for permanent flags or unique identifiers; furthermore
          there are known severe performance problems with the mh format.
     _________________________________________________________________

1.31 Is there support for qmail and the maildir format?

There is no support for qmail or the maildir format in our
          distribution, nor are there any plans to add such support.
          Maildir support may be available from third parties.
     _________________________________________________________________

1.32 Is there support for the Cyrus mailbox format?

No.
     _________________________________________________________________

1.33 Is this software Y2K compliant?

Please read the files Y2K and calendar.txt.
     _________________________________________________________________

2. What Do I Need to Build This Software?
     _________________________________________________________________

2.1 What do I need to build this software with SSL on UNIX?

You need to build and install OpenSSL first.
     _________________________________________________________________

2.2 What do I need to build this software with Kerberos V on UNIX?

You need to build and install MIT Kerberos first.
     _________________________________________________________________

2.3 What do I need to use a C++ compiler with this software to build
   my own application?

If you are building an application using the c-client library,
          use the new c-client.h file instead of including the other
          include files. It seems that c-client.h should define away all
          the troublesome names that conflict with C++.

If you use gcc, you may need to use -fno-operator-names as
          well.
     _________________________________________________________________

2.4 What do I need to build this software on Windows?

You need Microsoft Visual C++ 6.0, Visual C++ .NET, or Visual
          C# .NET (which you can buy from any computer store), along with
          the Microsoft Platform SDK (which you can download from
          Microsoft's web site).

You do not need to install the entire Platform SDK; it suffices
          to install just the Core SDK and the Internet Development SDK.
     _________________________________________________________________

2.5 What do I need to build this software on DOS?

It's been several years since we last attempted to do this. At
          the time, we used Microsoft C.
     _________________________________________________________________

2.6 Can't I use Borland C to build this software on the PC?

Probably not. If you know otherwise, please let us know.
     _________________________________________________________________

2.7 What do I need to build this software on the Mac?

It has been several years since we last attempted to do this.
          At the time, we used Symantec THINK C; but today you'll need a
          C compiler which allows segments to be more than 32K.
     _________________________________________________________________

2.8 What do I need to build this software on VMS?

You need the VMS C compiler, and either the Multinet or Netlib
          TCP.
     _________________________________________________________________

2.9 What do I need to build this software on TOPS-20?

You need the TOPS-20 KCC compiler.
     _________________________________________________________________

2.10 What do I need to build this software on Amiga or OS/2?

We don't know.
     _________________________________________________________________

2.11 What do I need to build this software on Windows CE?

This port is incomplete. Someone needs to finish it.
     _________________________________________________________________

3. Build and Configuration Questions
     _________________________________________________________________

3.1 How do I configure the IMAP and POP servers on UNIX?
   3.2 I built and installed the servers according to the BUILD
   instructions. It can't be that easy. Don't I need to write a config
   file?

For ordinary "vanilla" UNIX systems, this software is plug and
          play; just build it, install it, and you're done. If you have a
          modified system, then you may want to do additional work; most
          of this is to a single source code file (env_unix.c on UNIX
          systems). Read the file CONFIG for more details.

Yes, it's that easy. There are some additional options, such as
          SSL or Kerberos, which require additional steps to build. See
          the relevant questions below.
     _________________________________________________________________

3.3 How do I make the IMAP and POP servers look for INBOX at some
   place other than the mail spool directory?
   3.4 How do I make the IMAP server look for secondary folders at some
   place other than the user's home directory?

Please read the file CONFIG for discussion of this and other
          issues.
     _________________________________________________________________

3.5 How do I configure SSL?
   3.6 How do I configure TLS and the STARTTLS facility?

imap-2007 supports SSL and TLS client functionality on UNIX and
          32-bit Windows for IMAP, POP3, SMTP, and NNTP; and SSL and TLS
          server functionality on UNIX for IMAP and POP3.

UNIX SSL build requires that a third-party software package,
          OpenSSL, be installed on the system first. Read
          imap-2007/docs/SSLBUILD for more information.

SSL is supported via undocumented Microsoft interfaces in
          Windows 9x and NT4; and via standard interfaces in Windows
          2000, Windows Millenium, and Windows XP.
     _________________________________________________________________

3.7 How do I build/install OpenSSL and obtain/create certificates for
   use with SSL?

If you need help in doing this, try the contacts mentioned in
          the OpenSSL README. We do not offer support for OpenSSL or
          certificates.
     _________________________________________________________________

3.8 How do I configure CRAM-MD5 authentication?
   3.9 How do I configure APOP authentication?

CRAM-MD5 authentication is enabled in the IMAP and POP3 client
          code on all platforms. Read md5.txt to learn how to set up
          CRAM-MD5 and APOP authentication on UNIX and NT servers.

There is no support for APOP client authentication.
     _________________________________________________________________

3.10 How do I configure Kerberos V5?

imap-2007 supports client and server functionality on UNIX and
          32-bit Windows.

Kerberos V5 is supported by default in Windows 2000 builds:

nmake -f makefile.w2k

Other builds require that a third-party Kerberos package, e.g.
          MIT Kerberos, be installed on the system first.

To build with Kerberos V5 on UNIX, include
          EXTRAAUTHENTICATORS=gss in the make command line, e.g.

make lnp EXTRAAUTHENTICATORS=gss

To build with Kerberos V5 on Windows 9x, Windows Millenium, and
          NT4, use the "makefile.ntk" file instead of "makefile.nt":

nmake -f makefile.ntk
     _________________________________________________________________

3.11 How do I configure PAM for plaintext passwords?

On Linux systems, use the lnp port, e.g.

make lnp

On Solaris systems and other systems with defective PAM
          implementations, build with PASSWDTYPE=pmb, e.g.

make sol PASSWDTYPE=pmb

On all other systems, build with PASSWDTYPE=pam, e.g

make foo PASSWDTYPE=pam

If you build with PASSWDTYPE=pam and authentication does not
          work, try rebuilding (after a "make clean") with
          PASSWDTYPE=pmb.
     _________________________________________________________________

3.12 It looks like all I have to do to make the server use Kerberos is
   to build with PAM on my Linux system, and set it up in PAM for
   Kerberos passwords. Right?

Yes and no.

Doing this will make plaintext password authentication use the
          Kerberos password instead of the /etc/passwd password.

However, this will NOT give you Kerberos-secure authentication.
          See the answer to the How do I configure Kerberos V5? question
          for how to build with Kerberos-secure authentication.
     _________________________________________________________________

3.13 How do I configure Kerberos 5 for plaintext passwords?

Build with PASSWDTYPE=gss, e.g.

make sol PASSWDTYPE=gss

3.14 How do I configure AFS for plaintext passwords?

Build with PASSWDTYPE=afs, e.g

make sol PASSWDTYPE=afs
     _________________________________________________________________

3.15 How do I configure DCE for plaintext passwords?

Build with PASSWDTYPE=dce, e.g

make sol PASSWDTYPE=dce
     _________________________________________________________________

3.16 How do I configure the CRAM-MD5 database for plaintext passwords?

The CRAM-MD5 password database is automatically used for
          plaintext password if it exists.

Note that this is NOT CRAM-MD5-secure authentication. You
          probably want to consider disabling plaintext passwords for
          non-SSL/TLS sessions. See the next two questions.
     _________________________________________________________________

3.17 How do I disable plaintext passwords?

Server-level plaintext passwords can be disabled by setting
          PASSWDTYPE=nul, e.g.

make lnx EXTRAAUTHENTICATORS=gss PASSWDTYPE=nul

Note that you must have a CRAM-MD5 database installed or
          specify at least one EXTRAAUTHENTICATOR, otherwise it will not
          be possible to log in to the server.

When plaintext passwords are disabled, the IMAP server will
          advertise the LOGINDISABLED capability and the POP3 server will
          not advertise the USER capability.

3.18 How do I disable plaintext passwords on unencrypted sessions, but
   allow them in SSL or TLS sessions?

Do not set PASSWDTYPE=nul or SSLTYPE=unix. Set SSLTYPE=nopwd
          instead, e.g.

make lnx SSLTYPE=nopwd

When plaintext passwords are disabled, the IMAP server will
          advertise the LOGINDISABLED capability and the POP3 server will
          not advertise the USER capability.

Plaintext passwords will always be enabled in SSL sessions; the
          IMAP server will not advertise the LOGINDISABLED capability and
          the POP3 server will advertise the USER capability.

If the client does a successful start-TLS in a non-SSL session,
          plaintext passwords will be enabled, and a new CAPABILITY or
          CAPA command (which is required after start-TLS) will show the
          effect as in SSL sessions.
     _________________________________________________________________

3.19 How do I configure virtual hosts?

This is automatic, but with certain restrictions.

The most important one is that each virtual host must have its
          own IP address; otherwise the server has no way of knowing
          which virtual host is desired.

As distributed, the software uses a global password file; hence
          user "fred" on one virtual host is "fred" on all virtual hosts.
          You may want to modify the checkpw() routine to implement some
          other policy (e.g. separate password files).

Note that the security model assumes that all users have their
          own unique UNIX UID number. So if you use separate password
          files you should make certain that the UID numbers do not
          overlap between different files.

More advanced virtual host support may be available as patches
          from third parties.
     _________________________________________________________________

3.20 Why do I get compiler warning messages such as:
 passing arg 3 of `scandir' from incompatible pointer type
 Pointers are not assignment-compatible.
 Argument #4 is not the correct type.

during the build?

You can safely ignore these messages.

Over the years, the prototype for scandir() has changed, and
          thus is variant across different UNIX platforms. In particular,
          the definitions of the third argument (type select_t) and
          fourth argument (type compar_t) have changed over the years,
          the issue being whether or not the arguments to the functions
          pointed to by these function pointers are of type const or not.

The way that c-client calls scandir() will tend to generate
          these compiler warnings on newer systems such as Linux;
          however, it will still build. The problem with fixing the call
          is that then it won't build on older systems.
     _________________________________________________________________

3.21 Why do I get compiler warning messages such as
 Operation between types "void(*)(int)" and "void*" is not allowed.
 Function argument assignment between types "void*" and "void(*)(int)" is not a
llowed.
 Pointers are not assignment-compatible.
 Argument #5 is not the correct type.

during the build?

You can safely ignore these messages.

All known systems have no problem with casting a function
          pointer to/from a void* pointer, certain C compilers issue a
          compiler diagnostic because this facility is listed as a
          "Common extension" by the C standard:

K.5.7  Function pointer casts
  [#1] A pointer to an object or to void may be cast to a pointer
       to a function, allowing data to be invoked as a function (6.3.4).
  [#2] A pointer to a function may be cast to a pointer to an
       object or to void, allowing a function to be inspected or
       modified (for example, by a debugger) (6.3.4).

It may be just a "common extension", but this facility is
          relied upon heavily by c-client.
     _________________________________________________________________

3.22 Why do I get linker warning messages such as:
mtest.c:515: the `gets' function is dangerous and should not be used.

during the build? Isn't this a security bug?

You can safely ignore this message.

Certain linkers, most notably on Linux, give this warning
          message. It is indeed true that the traditional gets() function
          is not a safe one.

However, the mtest program is only a demonstration program, a
          model of a very basic application program using c-client. It is
          not something that you would install, much less run in any
          security-sensitive context.

mtest has numerous other shortcuts that you wouldn't want to do
          in a real application program.

The only "security bug" with mtest would be if it was run by
          some script in a security-sensitive context, but mtest isn't
          particularly useful for such purposes. If you wanted to write a
          script to automate some email task using c-client, you'd be
          better off using imapd instead of mtest.

mtest only has two legitimate uses. It's a useful testbed for
          me when debugging new versions of c-client, and it's useful as
          a model for someone writing a simple c-client application to
          see how the various calls work.

By the way, if you need a more advanced example of c-client
          programming than mtest (and you probably will), I recommend
          that you look at the source code for imapd and Pine.
     _________________________________________________________________

3.23 Why do I get linker warning messages such as:
 auth_ssl.c:92: the `tmpnam' function is dangerous and should not be used.

during the build? Isn't this a security bug?

You can safely ignore this message.

Certain linkers, most notably on Linux, give this warning
          message, based upon two known issues with tmpnam():

there can be a buffer overflow if an inadequate buffer is
                allocated.
                there can be a timing race caused by certain incautious
                usage of the return value.

Neither of these issues applies in the particular use that is
          made of tmpnam(). More importantly, the tmpnam() call is never
          executed on Linux systems.
     _________________________________________________________________

3.24 OK, suppose I see a warning message about a function being
   "dangerous and should not be used" for something other than this
   gets() or tmpnam() call?

Please forward the details for investigation.
     _________________________________________________________________

4. Operational Questions
     _________________________________________________________________

4.1 How can I enable anonymous IMAP logins?

Create the file /etc/anonymous.newsgroups. At the present time,
          this file should be empty. This will permit IMAP logins as
          anonymous as well as the ANONYMOUS SASL authenticator.
          Anonymous users have access to mailboxes in the #news., #ftp/,
          and #public/ namespaces only.
     _________________________________________________________________

4.2 How do I set up an alert message that each IMAP user will see?

Create the file /etc/imapd.alert with the text of the message.
          This text should be kept to one line if possible. Note that
          this will cause an alert to every IMAP user every time they
          initiate an IMAP session, so it should only be used for
          critical messages.
     _________________________________________________________________

4.3 How does the c-client library choose which of its several
   mechanisms to use to establish an IMAP connection to the server? I
   noticed that it can connect on port 143, port 993, via rsh, and via
   ssh.

c-client chooses how to establish an IMAP connection via the
          following rules:

+ If /ssl is specified, use an SSL connection. Fail otherwise.
          + Else if client is a UNIX system and "ssh server exec
            /etc/rimapd" works, use that
          + Else if /tryssl is specified and an SSL connection works, use
            that.
          + Else if client is a UNIX system and "rsh server exec
            /etc/rimapd" works, use that.
          + Else use a non-SSL connection.
     _________________________________________________________________

4.4 I am using a TLS-capable IMAP server, so I don't need to use /ssl
   to get encryption. However, I want to be certain that my session is
   TLS encrypted before I send my password. How to I do this?

Use the /tls option in the mailbox name. This will cause an
          error message and the connection to fail if the server does not
          negotiate STARTTLS.
     _________________________________________________________________

4.5 How do I use one of the alternative formats described in the
   formats.txt document? In particular, I hear that mbx format will give
   me better performance and allow shared access.

The rumors about mbx format being preferred are true. It is
          faster than the traditional UNIX mailbox format and permits
          shared access.

However, and this is very important, note that using an
          alternative mailbox format is an advanced facility, and only
          expert users should undertake it. If you don't understand any
          of the following notes, you may not be enough of an expert yet,
          and are probably better off not going this route until you are
          more comfortable with your understanding.

Some of the formats, including mbx, are only supported by the
          software based on the c-client library, and are not recognized
          by other mailbox programs. The "vi" editor will corrupt any mbx
          format mailbox that it encounters.

Another problem is that the certain formats, including mbx, use
          advanced file access and locking techniques that do not work
          reliably with NFS. NFS is not a real filesystem. Use IMAP
          instead of NFS for distributed access.

Each of the following steps are in escalating order of
          involvement. The further you go down this list, the more deeply
          committed you become:

+ The simplest way to create a mbx-format mailbox is to prefix
            the name with "#driver.mbx/" when creating a mailbox through
            c-client. For example, if you create "#driver.mbx/foo", the
            mailbox "foo" will be created in mbx format. Only use
            "#driver.mbx/" when creating the mailbox. At all other times,
            just use the name ("foo" in this example); the software will
            automatically select the driver for mbx whenever that mailbox
            is accessed without you doing anything else.
          + You can use the "mailutil copy" command to copy an existing
            mailbox to a new mailbox in mbx format. Read the man page
            provided with the mailutil program for details.
          + If you create an mbx-format INBOX, by creating
            "#driver.mbx/INBOX" (note that "INBOX" must be all
            uppercase), then subsequent access to INBOX by any c-client
            based application will use the mbx-format INBOX. Any mail
            delivered to the traditional format mailbox in the spool
            directory (e.g. /var/spool/mail/$USER) will automatically be
            copied into the mbx-format INBOX and the spool directory copy
            removed.
          + You can cause any newly-created mailboxes to be in mbx-format
            by default by changing the definition of
            CREATEPROTO=unixproto to be CREATEPROTO=mbxproto in
            src/osdep/unix/Makefile, then rebuilding the IMAP toolkit (do
            a "make clean" first). Do not change EMPTYPROTO, since mbx
            format mailboxes are never a zero-byte file. If you use Pine
            or the imap-utils, you should probably also rebuild them with
            the new IMAP toolkit too.
          + You can deliver directly to the mbx-format INBOX by use of
            the tmail or dmail programs. tmail is for direct invocation
            from sendmail (or whatever MTA program you use); dmail is for
            calls from procmail. Both of these programs have man pages
            which must be read carefully before making this change.

Most other servers (e.g. Cyrus) require use of a non-standard
          format. A full-fledged format conversion is not significantly
          different from what you have to do with other servers. The
          difference, which makes format conversion procedures somewhat
          more complicated with this server, is that there is no "all or
          nothing" requirement with this server. There are many points in
          between. A format conversion can be anything from a single
          mailbox or single user, to systemwide.

This is good in that you can decide how far to go, or do the
          steps incrementally as you become more comfortable with the
          result. On the other hand, there's no "One True Way" which can
          be boiled down to a simple set of pedagogical instructions.

A number of sites have done full-fledged format conversions,
          and are reportedly quite happy with the results. Feel free to
          ask in the comp.mail.imap newsgroup or the imap-uw mailing
          list for advice or help.
     _________________________________________________________________

4.6 How do I set up shared mailboxes?

At the simplest level, a shared mailbox is one which has UNIX
          file and directory protections which permit multiple users to
          access it. What this means is that your existing skills and
          tools to create and manage shared files on your UNIX system
          apply to shared mailboxes; e.g.

chmod 666 mailbox

You may want to consider the use of a mailbox format which
          permits multiple simultaneous read/write sessions, such as the
          mbx format. The traditional UNIX format only allows one
          read/write session to a mailbox at a time.

An additional convenience item are three system directories,
          which can be set up for shared namespaces. These are: #ftp,
          #shared, and #public, and are defined by creating the
          associated UNIX users and home directories as described below.

#ftp/ refers to the anonymous ftp filesystem exported by the
          ftp server, and is equivalent to the home directory for UNIX
          user "ftp". For example, #ftp/foo/bar refers to the file
          /foo/bar in the anonymous FTP filesystem, or ~ftp/foo/bar for
          normal users. Anonymous FTP files are available to anonymous
          IMAP logins. By default, newly-created files in #ftp/ are
          protected 644.

#public/ refers to an IMAP toolkit convention called "public"
          files, and is equivalent to the home directory for UNIX user
          "imappublic". For example, #public/foo/bar refers to the file
          ~imappublic/foo/bar. Public files are available to anonymous
          IMAP logins. By default, newly-created files in #public are
          created with protection 0666.

#shared/ refers to an IMAP toolkit convention called "shared"
          files, and is equivalent to the home directory for UNIX user
          "imapshared". For example, #shared/foo/bar refers to the file
          ~imapshared/foo/bar. Shared files are not available to
          anonymous IMAP logins. By default, newly-created files in
          #shared are created with protection 0660.
     _________________________________________________________________

4.7 How can I make the server syslogs go to someplace other than the
   mail syslog?

The openlog() call that sets the syslog facility is in
          src/osdep/unix/env_unix.c in routine server_init(). You need to
          edit this file to change the syslog facility from LOG_MAIL to
          the facility you want, then rebuild. You also need to set up
          your /etc/syslog.conf properly.

Refer to the man pages for syslog and syslogd for more
          information on what the available syslog facilities are and how
          to configure syslogs. If you still don't understand what to do,
          find a UNIX system expert.
     _________________________________________________________________

5. Security Questions
     _________________________________________________________________

5.1 I see that the IMAP server allows access to arbitary files on the
   system, including /etc/passwd! How do I disable this?

You should not worry about this if your IMAP users are allowed
          shell access. The IMAP server does not permit any access that
          the user can not have via the shell.

If, and only if, you deny your IMAP users shell access, you may
          want to consider one of three choices. Note that these choices
          reduce IMAP functionality, and may have undesirable side
          effects. Each of these choices involves an edit to file
          src/osdep/unix/env_unix.c

The first (and recommended) choice is to set restrictBox as
          described in file CONFIG. This will disable access to the
          filesystem root, to other users' home directory, and to
          superior directory.

The second (and strongly NOT recommended) choice is to set
          closedBox as described in file CONFIG. This puts each IMAP
          session into a so-called "chroot jail", and thus setting this
          option is extremely dangerous; it can make your system much
          less secure and open to root compromise attacks. So do not use
          this option unless you are absolutely certain that you
          understand all the issues of a "chroot jail."

The third choice is to rewrite routine mailboxfile() to
          implement whatever mapping from mailbox name to filesystem name
          (and restrictions) that you wish. This is the most general
          choice. As a guide, you can see at the start of routine
          mailboxfile() what the restrictBox choice does.
     _________________________________________________________________

5.2 I've heard that IMAP servers are insecure. Is this true?

There are no known security problems in this version of the
          IMAP toolkit, including the IMAP and POP servers. The IMAP and
          POP servers limit what can be done while not logged in, and as
          part of the login process discard all privileges except those
          of the user.

As with other software packages, there have been buffer
          overflow vulnerabilities in past versions. All known problems
          of this nature are fixed in this version.

There is every reason to believe that the bad guys are engaged
          in an ongoing effort to find vulnerabilities in the IMAP
          toolkit. We look for such problems, and when one is found we
          fix it.

It's unfortunate that any vulnerabilities existed in past
          versions, and we're doing my best to keep the IMAP toolkit free
          of vulnerabilities. No new vulnerabilities have been discovered
          in quite a while, but efforts will not be relaxed.

Beware of vendors who claim that their implementations can not
          have vulnerabilities.
     _________________________________________________________________

5.3 How do I know that I have the most secure version of the server?

The best way is to keep your server software up to date. The
          bad guys are always looking for ways to crack software, and
          when they find one, let all their friends know.

Oldtimers used to refer to a concept of software rot: if your
          software hasn't been updated in a while, it would "rot" -- tend
          to acquire problems that it didn't have when it was new.

The latest release version of the IMAP toolkit is always
          available at ftp://ftp.cac.washington.edu/mail/imap.tar.Z
     _________________________________________________________________

5.4 I see all these strcpy() and sprintf() calls, those are unsafe,
   aren't they?

Yes and no.

It can be unsafe to do these calls if you do not know that the
          string being written will fit in the buffer. However, they are
          perfectly safe if you do know that.

Beware of programmers who advocate doing a brute-force change
          of all instances of

strcpy (s,t);

strncpy (s,t,n)[n] = '\0';

and similar measures in the name of "fixing all possible buffer
          overflows."

There are examples in which a security bug was introduced
          because of this type of "fix", due to the programmer using the
          wrong value for n. In one case, the programmer thought that n
          was larger than it actually was, causing a NUL to be written
          out of the buffer; in another, n was too small, and a security
          credential was truncated.

What is particularly ironic was that in both cases, the
          original strcpy() was safe, because the size of the source
          string was known to be safe.

With all this in mind, the software has been inspected, and it
          is believed that all places where buffer overflows can happen
          have been fixed. The strcpy()s that are still are in the code
          occur after a size check was done in some other way.

Note that the common C idiom of

*s++ = c;

is just as vulnerable to buffer overflows. You can't cure
          buffer overflows by outlawing certain functions, nor is it
          desirable to do so; sometimes operations like strcpy()
          translate into fast machine instructions for better
          performance.

Nothing replaces careful study of code. That's how the bad guys
          find bugs. Security is not accomplished by means of brute-force
          shortcuts.
     _________________________________________________________________

5.5 Those /tmp lock files are protected 666, is that really right?

Yes. Shared mailboxes won't work otherwise. Also, you get into
          accidental denial of service problems with old lock files left
          lying around; this happens fairly frequently.

The deliberate mischief that can be caused by fiddling with the
          lock files is small-scale; harassment level at most. There are
          many -- and much more effective -- other ways of harassing
          another user on UNIX. It's usually not difficult to determine
          the culprit.

Before worrying about deliberate mischief, worry first about
          things happening by accident!
     _________________________________________________________________

6. Why Did You Do This Strange Thing? Questions
     _________________________________________________________________

6.1 Why don't you use GNU autoconfig / automake / autoblurdybloop?

Autoconfig et al are not available on all the platforms where
          the IMAP toolkit is supported; and do not work correctly on
          some of the platforms where they do exist. Furthermore, these
          programs add another layer of complexity to an already complex
          process.

Coaxing software that uses autoconfig to build properly on
          platforms which were not specifically considered by that
          software wastes an inordinate amount of time. When (not if)
          autoconfig fails to do the right thing, the result is an
          inpenetrable morass to untangle in order to find the problem
          and fix it.

The concept behind autoconfig is good, but the execution is
          flawed. It rarely does the right thing on a platform that
          wasn't specifically considered. Human life is too short to
          debug autoconfig problems, especially since the current
          mechanism is so much easier.
     _________________________________________________________________

6.2 Why do you insist upon a build with -g? Doesn't it waste disk and
   memory space?

From time to time a submitted port has snuck in without -g.
          This has always ended up causing problems. There are only two
          valid excuses for not using -g in a port:

+ The compiler does not support -g
          + An alternate form of -g is needed with optimization, e.g.
            -g3.

There will be no new ports added without -g (or a suitable
          alternative) being set.

-g has not been arbitrarily added to the ports which do not
          currently have it because we don't know if doing so would break
          the build. However, any support issues with one of those port
          will lead to the correct -g setting being determined and
          permanently added.

Processors are fast enough (and disk space is cheap enough)
          that -g should be automatic in all compilers with no way of
          turning it off, and /bin/strip should be a symlink to
          /bin/true. Human life is too short to deal with binaries built
          without -g. Such binaries should be a bad memory of the days of
          KIPS processors and disks that costs several dollars per
          kilobyte.
     _________________________________________________________________

6.3 Why don't you make c-client a shared library?

All too often, shared libraries create far more problems than
          they solve.

Remember that you only gain the benefit of a shared library
          when there are multiple applications which use that shared
          library. Even without shared libraries, on most modern
          operating systems (and many ancient ones too!) applications
          will share their text segments between across multiple
          processes running the same application. This means that if your
          system only runs one application (e.g. imapd) that uses the
          c-client library, then you gain no benefit from making c-client
          a shared library even if it has 100 imapd processes. You will,
          however suffer added complexity.

If you have a server system that just runs imapd and ipop3d,
          then making c-client a shared library will save just one copy
          of c-client no matter how many IMAP/POP3 processes are running.

The problem with shared libraries is that you have to keep
          around a copy of the library every time something changes in
          the library that would affect the interface the library
          presents to the application. So, you end up having many copies
          of the same shared library.

If you don't keep multiple copies of the shared library, then
          one of two things happens. If there was proper versioning, then
          you'll get a message such as "cannot open shared object file"
          or "minor versions don't match" and the application won't run.
          Otherwise, the application will run, but will fail in
          mysterious ways.

Several sites and third-party distributors have modified the
          c-client makefile in order to make c-client be a shared
          library. When (not if) a c-client based application fails in
          mysterious ways because of a library compatibility problem, the
          result is a bug report. A lot of time and effort ends up
          getting wasted investigating such bug reports.

Memory is so cheap these days that it's not worth it. Human
          life is too short to deal with shared library compatibility
          problems.
     _________________________________________________________________

6.4 Why don't you use iconv() for internationalization support?

iconv() is not ubiquitous enough.
     _________________________________________________________________

6.5 Why is the IMAP server connected to the home directory by default?

The IMAP server has no way of knowing what you might call
          "mail" as opposed to "some other file"; in fact, you can use
          IMAP to access any file.

The IMAP server also doesn't know whether your preferred
          subdirectory for mailbox files is "mail/", ".mail/", "Mail/",
          "Mailboxes/", or any of a zillion other possibilities. If one
          such name were chosen, it would undoubtably anger the partisans
          of all the other names.

It is possible to modify the software so that the default
          connected directory is someplace else. Please read the file
          CONFIG for discussion of this and other issues.
     _________________________________________________________________

6.6 I have a Windows system. Why isn't the server plug and play for
   me?

There is no standard for how mail is stored on Windows; nor a
          single standard SMTP server. The closest to either would be the
          SMTP server in Microsoft's IIS.

So there's no default by which to make assumptions. As the
          software is set up, it assumes that the each user has an
          Windows login account and private home directory, and that mail
          is stored on that home directory as files in one of the popular
          UNIX formats. It also assumes that there is some tool
          equivalent to inetd on UNIX that does the TCP/IP listening and
          server startup.

Basically, unless you're an email software hacker, you probably
          want to look elsewhere if you want IMAP/POP servers for
          Windows.
     _________________________________________________________________

6.7 I looked at the UNIX SSL code and saw that you have the SSL data
   payload size set to 8192 bytes. SSL allows 16K; why aren't you using
   the full size?

This is to avoid an interoperability problem with:

+ PC IMAP clients that use Microsoft's SChannel.DLL (SSPI) for
            SSL support
          + Microsoft Exchange server (which also uses SChannel).

SChannel has a bug that makes it think that the maximum SSL
          data payload size is 16379 bytes -- 5 bytes too small. Thus,
          c-client has to make sure that it never transmits full sized
          SSL packets.

The reason for using 8K (as opposed to, say, 16379 bytes, or
          15K, or...) is that it corresponds with the TCP buffer size
          that the software uses elsewhere for input; there's a slight
          performance benefit to having the two sizes correspond or at
          least be a multiple of each other. Also, it keeps the size as a
          power of two, which might be significant on some platforms.

There wasn't a significant difference that we could measure
          between 8K and 15K.

Microsoft has developed a hotfix for this bug. Look up MSKB
          article number 300562. Contrary to the article text which
          implies that this is a Pine issue, this bug also affects
          Microsoft Exchange server with any client that transmits
          full-sized SSL payloads.
     _________________________________________________________________

6.8 Why is an mh format INBOX called #mhinbox instead of just INBOX?

It's a long story. In brief, the mh format driver is less
          functional than any of the other drivers. It turned out that
          there were some users (including high-level administrators) who
          tried mh years ago and no longer use it, but still had an mh
          profile left behind.

When the mh driver used INBOX, it would see the mh profile, and
          proceed to move the user's INBOX into the mh format INBOX. This
          caused considerable confusion as some things stopped working.
     _________________________________________________________________

6.9 Why don't you support the maildir format?

It is technically difficult to support maildir in IMAP while
          maintaining acceptable performance, robustness, following the
          requirements of the IMAP protocol specification, and following
          the requirements of maildir.

No one has succeeded in accomplishing all four together. The
          various maildir drivers offered as patches all have these
          problems. The problem is exacerbated because this
          implementation supports multiple formats; consequently this
          implementation can't make any performance shortcuts by assuming
          that all the world is maildir.

We can't do a better job than the maildir fan community has
          done with their maildir drivers. Similarly, if the maildir fan
          community provides the maildir driver, they take on the
          responsibility for answering maildir-specific support
          questions. This is as it should be, and that is why maildir
          support is left to the maildir fan community.
     _________________________________________________________________

6.10 Why don't you support the Cyrus format?

There's no point to doing so. An implementation which supports
          multiple formats will never do as well as one which is
          optimized to support one single format.

If you want to use Cyrus mailbox format, you should use the
          Cyrus server, which is the native implementation of that format
          and is specifically optimized for that format. That's also why
          Cyrus doesn't implement any other format.
     _________________________________________________________________

6.11 Why is it creating extra forks on my SVR4 system?

This is because your system only has fcntl() style locking and
          not flock() style locking. fcntl() locking has a design flaw
          that causes a close() to release any locks made by that process
          on the file opened on that file descriptor, even if the lock
          was made on a different file descriptor.

This design flaw causes unexpected loss of lock, and consequent
          mailbox corruption. The workaround is to do certain "dangerous
          operations" in another fork, thus avoiding doing a close() in
          the vulnerable fork.

The best way to solve this problem is to upgrade your SVR4
          (Solaris, AIX, HP-UX, SGI) or OSF/1 system to a more advanced
          operating system, such as Linux or BSD. These more advanced
          operating systems have fcntl() locking for compatibility with
          SVR4, but also have flock() locking.

Beware of certain SVR4 systems, such as AIX, which have an
          "flock()" function in their C library that is just a jacket
          that does an fcntl() lock. This is not a true flock(), and has
          the same design flaw as fcntl().
     _________________________________________________________________

6.12 Why are you so fussy about the date/time format in the internal
   "From " line in traditional UNIX mailbox files? My other mail program
   just considers every line that starts with "From " to be the start of
   the message.

You just answered your own question. If any line that starts
          with "From " is treated as the start of a message, then every
          message text line which starts with "From " has to be quoted
          (typically by prefixing a ">" character). People complain about
          this -- "why did a > get stuck in my message?"

So, good mail reading software only considers a line to be a
          "From " line if it follows the actual specification for a
          "From " line. This means, among other things, that the day of
          week is fixed-format: "May 14", but "May  7" (note the extra
          space) as opposed to "May 7". ctime() format for the date is
          the most common, although POSIX also allows a numeric timezone
          after the year. For compatibility with ancient software, the
          seconds are optional, the timezone may appear before the year,
          the old 3-letter timezones are also permitted, and "remote from
          xxx" may appear after the whole thing.

Unfortunately, some software written by novices use other
          formats. The most common error is to have a variable-width day
          of month, perhaps in the erroneous belief that RFC 2822 (or RFC
          822) defines the format of the date/time in the "From " line
          (it doesn't; no RFC describes internal formats). I've seen a
          few other goofs, such as a single-digit second, but these are
          less common.

If you are writing your own software that writes mailbox files,
          and you really aren't all that savvy with all the ins and outs
          and ancient history, you should seriously consider using the
          c-client library (e.g. routine mail_append()) instead of doing
          the file writes yourself. If you must do it yourself, use
          ctime(), as in:

fprintf (mbx,"From %s@%h %s",user,host,ctime (time (0)));

rather than try to figure out a good format yourself. ctime()
          is the most traditional format and nobody will flame you for
          using it.
     _________________________________________________________________

6.13 Why is traditional UNIX format the default format?

Compatibility with the past 30 or so years of UNIX history.
          This server is the only one that completely interoperates with
          legacy UNIX mail tools.
     _________________________________________________________________

6.14 Why do you write this "DON'T DELETE THIS MESSAGE -- FOLDER
   INTERNAL DATA" message at the start of traditional UNIX and MMDF
   format mailboxes?

This pseudo-message serves two purposes.

First, it establishes the mailbox format even when the mailbox
          has no messages. Otherwise, a mailbox with no messages is a
          zero-byte file, which could be one of several formats.

Second, it holds mailbox metadata used by IMAP: the UID
          validity, the last assigned UID, and mailbox keywords. Without
          this metadata, which must be preserved even when the mailbox
          has no messages, the traditional UNIX format wouldn't be able
          to support the full capabilities of IMAP.
     _________________________________________________________________

6.15 Why don't you stash the mailbox metadata in the first real
   message of the mailbox instead of writing this fake FOLDER INTERNAL
   DATA message?

In fact, that is what is done if the mailbox is non-empty and
          does not already have a FOLDER INTERNAL DATA message.

One problem with doing that is that if some external program
          removes the first message, the metadata is lost and must be
          recreated, thus losing any prior UID or keyword list status
          that IMAP clients may depend upon.

Another problem is that this doesn't help if the last message
          is deleted. This will result in an empty mailbox, and the
          necessity to create a FOLDER INTERNAL DATA message.
     _________________________________________________________________

6.16 Why aren't "dual-use" mailboxes the default?

Compatibility with the past 30 or so years of UNIX history, not
          to mention compatibility with user expectations when using
          shell tools.
     _________________________________________________________________

6.17 Why do you use ucbcc to build on Solaris?

It is a long, long story about why cc is set to ucbcc. You need
          to invoke the C compiler so that it links with the SVR4
          libraries and not the BSD libraries, otherwise readdir() will
          return the wrong information.

Of all the names in the most common path, ucbcc is the only
          name to be found (on /usr/ccs/bin) that points to a suitable
          compiler. cc is likely to be /usr/ucb/cc which is absolutely
          not the compiler that you want. The real SVR4 cc is probably
          something like /opt/SUNWspro/bin/cc which is rarely in anyone's
          path by default.

ucbcc is probably a link to acc, e.g.
          /opt/SUNWspro/SC4.0/bin/acc, and is the UCB C compiler using
          the SVR4 libraries.

If ucbcc isn't on your system, then punt on the SUN C compiler
          and use gcc instead (the gso port instead of the sol port).

If, in spite of all the above warnings, you choose to change
          "ucbcc" to "cc", you will probably find that the -O2 needs to
          be changed to -O. If you don't get any error messages with -O2,
          that's a pretty good indicator that you goofed and are running
          the compiler that will link with the BSD libraries.

To recap:

+ The sol port is designed to be built using the UCB compiler
            using the SVR4 libraries. This compiler is "ucbcc", which is
            lunk to acc. You use -O2 as one of the CFLAGS.
          + If you build the sol port with the UCB compiler using the BSD
            libraries, you will get no error messages but you will get
            bad binaries (the most obvious symptom is dropping the first
            two characters return filenames from the imapd LIST command.
            This compiler also uses -O2, and is very often what the user
            gets from "cc". BEWARE
          + If you build the sol port with the real SVR4 compiler, which
            is often hidden away or unavailable on many systems, then you
            will get errors from -O2 and you need to change that to -O.
            But you will get a good binary. However, you should try it
            with -O2 first, to make sure that you got this compiler and
            not the UCB compiler using BSD libraries.
     _________________________________________________________________

6.18 Why should I care about some old system with BSD libraries? cc is
   the right thing on my Solaris system!

Because there still are sites that use such systems. On those
          systems, the assumption that "cc" does the right thing will
          lead to corrupt binaries with no error message or other warning
          that anything is amiss.

Too many sites have fallen victim to this problem.
     _________________________________________________________________

6.19 Why do you insist upon writing .lock files in the spool
   directory?

Compatibility with the past 30 years of UNIX software which
          deals with the spool directory, especially software which
          delivers mail. Otherwise, it is possible to lose mail.
     _________________________________________________________________

6.20 Why should I care about compatibility with the past?

This is one of those questions in which the answer never
          convinces those who ask it. Somehow, everybody who ever asks
          this question ends up answering it for themselves as they get
          older, with the very answer that they rejected years earlier.
     _________________________________________________________________

7. Problems and Annoyances
     _________________________________________________________________

7.1 Help! My INBOX is empty! What happened to my messages?

If you are seeing "0 messages" when you open INBOX and you know
          you have messages there (and perhaps have looked at your mail
          spool file and see that messages are there), then probably
          there is something wrong with the very first line of your mail
          spool file. Make sure that the first five bytes of the file are
          "From ", followed by an email address and a date/time in
          ctime() format, e.g.:

From fred@foo.bar Mon May  7 20:54:30 2001
     _________________________________________________________________

7.2 Help! All my messages in a non-INBOX mailbox have been
   concatenated into one message which claims to be from me and has a
   subject of the file name of the mailbox! What's going on?

Something wrong with the very first line of the mailbox. Make
          sure that the first five bytes of the file are "From ",
          followed by an email address and a date/time in ctime() format,
          e.g.:

From fred@foo.bar Mon May  7 20:54:30 2001
     _________________________________________________________________

7.3 Why do I get the message: CREATE failed: Can't create mailbox node
   xxxxxxxxx: File exists and how do I fix it?

See the answer to the Are hierarchical mailboxes supported?
          question.
     _________________________________________________________________

7.4 Why can't I log in to the server? The user name and password are
   right!

There are a myriad number of possible answers to this question.
          The only way to say for sure what is wrong is run the server
          under a debugger such as gdb while root (yes, you must be root)
          with a breakpoint at routines checkpw() and loginpw(), then
          single-step until you see which test rejected you. The server
          isn't going to give any error messages other than "login
          failed" in the name of not giving out any unnecessary
          information to unauthorized individuals.

Here are some of the more common reasons why login may fail:

+ You didn't really give the correct user name and/or password.
          + Your client doesn't send the LOGIN command correctly; for
            example, IMAP2 clients won't send a password containing a "*"
            correctly to an IMAP4 server.
          + If you have set up a CRAM-MD5 database, remember that the
            password used is the one in the CRAM-MD5 database, and
            furthermore that there must also be an entry in /etc/passwd
            (but the /etc/passwd password is not used).
          + If you are using PAM, have you created a service file for the
            server in /etc/pam.d?
          + If you are using shadow passwords, have you used an
            appropriate port when building? In particular, note that
            "lnx" is for Linux systems without shadow passwords; you
            probably want "slx" or "lnp" instead.
          + If your system has account or password expirations, check to
            see that the expiration date hasn't passed.
          + You can't log in as root or any other UID 0 user. This is for
            your own safety, not to mention the fact that the servers use
            UID 0 as meaning "not logged in".
     _________________________________________________________________

7.5 Help! My load average is soaring and I see hundreds of POP and
   IMAP servers, many logged in as the same user!

Certain inferior losing GUI mail reading programs have a
          "synchronize all mailboxes at startup" (IMAP) or "check for new
          mail every second" (POP) feature which causes a rapid and
          unchecked spawning of servers.

This is not a problem in the server; the client is really
          asking for all those server sessions. Unfortunately, there
          isn't much that the POP and IMAP servers can do about it; they
          don't spawned themselves.

Some sites have added code to record the number of server
          sessions spawned per user per hour, and disable login for a
          user who has exceeded a predetermined rate. This doesn't stop
          the servers from being spawned; it just means that a server
          session will commit suicide a bit faster.

Another possibility is to detect excessive server spawning
          activity at the level where the server is spawned, which would
          be inetd or possibly tcpd. The problem here is that this is a
          hard time to quantify. 50 sessions in a minute from a
          multi-user timesharing system may be perfectly alright, whereas
          10 sessions a minute from a PC may be too much.

The real solution is to fix the client configuration, by
          disabling those evil features. Also tell the vendors of those
          clients how you feel about distributing denial-of-service
          attack tools in the guise of mail reading programs.
     _________________________________________________________________

7.6 Why does mail disappear even though I set "keep mail on server"?
   7.7 Why do I get the message Moved ##### bytes of new mail to
   /home/user/mbox from /var/spool/mail/user and why did this happen?

This is probably caused by the mbox driver. If the file "mbox"
          exists on the user's home directory and is in UNIX mailbox
          format, then when INBOX is opened this file will be selected as
          INBOX instead of the mail spool file. Messages will be
          automatically transferred from the mail spool file into the
          mbox file.

To disable this behavior, delete "mbox" from the EXTRADRIVERS
          list in the top-level Makefile and rebuild. Note that if you do
          this, users won't be able to access the messages that have
          already been moved to mbox unless they open mbox instead of
          INBOX.
     _________________________________________________________________

7.8 Why isn't it showing the local host name as a fully-qualified
   domain name?
   7.9 Why is the local host name in the From/Sender/Message-ID headers
   of outgoing mail not coming out as a fully-qualified domain name?

Your UNIX system is misconfigured. The entry for your system in
          /etc/hosts must have the fully-qualified domain name first,
          e.g.

105.69.1.234   myserver.example.com myserver

A common mistake of novice system administrators is to have the
          short name first, e.g.

105.69.1.234   myserver myserver.example.com

or to omit the fully qualified domain name entirely, e.g.

105.69.1.234   myserver

The result of this is that when the IMAP toolkit does a
          gethostbyname() call to get the fully-qualified domain name, it
          would get "myserver" instead of "myserver.example.com".

On some systems, a configuration file (typically named
          /etc/svc.conf, /etc/netsvc.conf, or /etc/nsswitch.conf) can be
          used to configure the system to use the domain name system
          (DNS) instead of /etc/hosts, so it doesn't matter if /etc/hosts
          is misconfigured.

Check the man pages for gethostbyname, hosts, svc, and/or
          netsvc for more information.

Unfortunately, certain vendors, most notably SUN, have failed
          to make this clear in their documentation. Most of SUN's
          documentation assumes a corporate network that is not connected
          to the Internet.

net.folklore once (late 1980s) held that the proper procedure
          was to append the results of getdomainname() to the name
          returned by gethostname(), and some versions of sendmail
          configuration files were distributed that did this. This was
          incorrect; the string returned from getdomainname() is the
          Yellow Pages (a.k.a NIS) domain name, which is a completely
          different (albeit unfortunately named) entity from an Internet
          domain. These were often fortuitously the same string, except
          when they weren't. Frequently, this would result in host names
          with spuriously doubled domain names, e.g.

myserver.example.com.example.com

This practice has been thoroughly discredited for many years,
          but folklore dies hard.
     _________________________________________________________________

7.10 What does the message: Mailbox vulnerable - directory
   /var/spool/mail must have 1777 protection mean? How can I fix this?

In order to update a mailbox in the default UNIX format, it is
          necessary to create a lock file to prevent the mailer from
          delivering mail while an update is in progress. Some systems
          use a directory protection of 775, requiring that all mail
          handling programs be setgid mail; or of 755, requiring that all
          mail handling programs be setuid root.

The IMAP toolkit does not run with any special privileges, and
          I plan to keep it that way. It is antithetical to the concept
          of a toolkit if users can't write their own programs to use it.
          Also, I've had enough bad experiences with security bugs while
          running privileged; the IMAP and POP servers have to be root
          when not logged in, in order to be able to log themselves in. I
          don't want to go any deeper down that slippery slope.

Directory protection 1777 is secure enough on most well-managed
          systems. If you can't trust your users with a 1777 mail spool
          (petty harassment is about the limit of the abuse exposure),
          then you have much worse problems then that.

If you absolutely insist upon requiring privileges to create a
          lock file, external file locking can be done via a setgid mail
          program named /etc/mlock (this is defined by LOCKPGM in the
          c-client Makefile). If the toolkit is unable to create a
          <...mailbox...>.lock file in the directory by itself, it will
          try to call mlock to do it. I do not recommend doing this for
          performance reasons.

A sample mlock program is included as part of imap-2007. We
          have tried to make this sample program secure, but it has not
          been thoroughly audited.
     _________________________________________________________________

7.11 What does the message: Mailbox is open by another process, access
   is readonly mean? How do I fix this?

A problem occurred in applying a lock to a /tmp lock file.
          Either some other program has the mailbox open and won't
          relenquish it, or something is wrong with the protection of
          /tmp or the lock.

Make sure that the /tmp directory is protected 1777. Some
          security scripts incorrectly set the protection of the /tmp
          directory to 775, which disables /tmp for all non-privileged
          programs.
     _________________________________________________________________

7.12 What does the message: Can't get write access to mailbox, access
   is readonly mean?

The mailbox file is write-protected against you.
     _________________________________________________________________

7.13 I set my POP3 client to "delete messages from server" but they
   never get deleted. What is wrong?

Make sure that your mailbox is not read-only: that the mailbox
          is owned by you and write enabled (protection 0600), and that
          the /tmp directory is longer world-writeable. /tmp must be
          world-writeable because lots of applications use it for scratch
          space. To fix this, do

chmod 1777 /tmp

as root.

Make sure that your POP3 client issues a QUIT command when it
          finishes. The POP3 protocol specifies that deletions are
          discarded unless a proper QUIT is done.

Make sure that you are not opening multiple POP3 sessions to
          the same mailbox. It is a requirement of the POP3 protocol than
          only one POP3 session be in effect to a mailbox at a time,
          however some, poorly-written POP3 clients violate this. Also,
          some background "check for new mail" tasks also cause a
          violation. See the answer to the What does the syslog message:
          Killed (lost mailbox lock) user=... host=... mean? question for
          more details.
     _________________________________________________________________

7.14 What do messages such as:
 Message ... UID ... already has UID ...
 Message ... UID ... less than ...
 Message ... UID ... greater than last ...
 Invalid UID ... in message ..., rebuilding UIDs

mean?

Something happened to corrupt the unique identifier regime in
          the mailbox. In traditional UNIX-format mailboxes, this can
          happen if the user deleted the "DO NOT DELETE" internal
          message.

This problem is relatively harmless; a new valid unique
          identifier regime will be created. The main effect is that any
          references to the old UIDs will no longer be useful.

So, unless it is a chronic problem or you feel like debugging,
          you can safely ignore these messages.
     _________________________________________________________________

7.15 What do the error messages:
 Unable to read internal header at ...
 Unable to find CRLF at ...
 Unable to parse internal header at ...
 Unable to parse message date at ...
 Unable to parse message flags at ...
 Unable to parse message UID at ...
 Unable to parse message size at ...
 Last message (at ... ) runs past end of file ...

mean? I am using mbx format.

The mbx-format mailbox is corrupted and needs to be repaired.

You should make an effort to find out why the corruption
          happened. Was there an obvious system problem (crash or disk
          failure)? Did the user accidentally access the file via NFS?
          Mailboxes don't get corrupted by themselves; something caused
          the problem.

Some people have developed automated scripts, but if you're
          comfortable using emacs it's pretty easy to fix it manually. Do
          not use vi or any other editor unless you are certain that
          editor can handle binary!!!

If you are not comfortable with emacs, or if the file is too
          large to read with emacs, see the "step-by-step" technique
          later on for another way of doing it.

After the word "at" in the error message is the byte position
          it got to when it got unhappy with the file, e.g. if you see:

Unable to parse internal header at 43921: ne bombastic blurdybloop

The problem occurs at the 43,931 byte in the file. That's the
          point you need to fix. c-client is expecting an internal header
          at that byte number, looking something like:

6-Jan-1998 17:42:24 -0800,1045;000000100001-00000001

The format of this internal line is:

dd-mmm-yyyy hh:mm:ss +zzzz,ssss;ffffffffFFFF-UUUUUUUU

The only thing that is variable is the "ssss" field, it can be
          as many digits as needed. All other fields (inluding the "dd")
          are fixed width. So, the easiest thing to do is to look forward
          in the file for the next internal header, and delete everything
          from the error point to that internal header.

Here's what to do if you want to be smarter and do a little bit
          more work. Generally, you're in the middle of a message, and
          there's nothing wrong with that message. The problem happened
          in the *previous* message. So, search back to the previous
          internal header. Now, remember that "ssss" field? That's the
          size of that message.

Mark where you are in the file, move the cursor to the line
          after the internal header, and skip that many bytes ("ssss")
          forward. If you're at the point of the error in the file, then
          that message is corrupt. If you're at a different point, then
          perhaps the previous message is corrupt and has a too long size
          count that "ate" into this message.

Basically, what you need to do is make sure that all those size
          counts are right, and that moving "ssss" bytes from the line
          after the internal header will land you at another internal
          header.

Usually, once you know what you're looking at, it's pretty easy
          to work out the corruption, and the best remedial action.
          Repair scripts will make the problem go away but may not always
          do the smartest/best salvage of the user's data. Manual repair
          is more flexible and usually preferable.

Here is a step-by-step technique for fixing corrupt mbx files
          that's a bit cruder than the procedure outlined above, but
          works for any size file.

In this example, suppose that the corrupt file is INBOX, the
          error message is

Unable to find CRLF at 132551754

and the size of the INBOX file is 132867870 bytes.

The first step is to split the mailbox file at the point of the
          error:

+ Rename the INBOX file to some other name, such as INBOX.bad.
          + Copy the first 132,551,754 bytes of INBOX.bad to another
            file, such as INBOX.new.
          + Extract the trailing 316,116 bytes (132867870-132551754) of
            INBOX.bad into another file, such as INBOX.tail.
          + You no longer need INBOX.bad. Delete it.

In other words, use the number from the "Unable to find CRLF
          at" as the point to split INBOX into two new files, INBOX.new
          and INBOX.tail.

Now, remove the erroneous data:

+ Verify that you can open INBOX.new in IMAP or Pine.
          + The last message of INBOX.new is probably corrupted. Copy it
            to another file, such as badmsg.1, then delete and expunge
            that last message from INBOX.new
          + Locate the first occurance of text in INBOX.tail which looks
            like an internal header, as described above.
          + Remove all the text which occurs prior to that point, and
            place it into another file, such as badmsg.2. Note that in
            the case of a single digit date, there is a leading space
            which must not be removed (e.g. " 6-Nov-2001" not
            "6-Nov-2001").

Reassemble the mailbox:

+ Append INBOX.tail to INBOX.new.
          + You no longer need INBOX.tail. Delete it.
          + Verify that you can open INBOX.new in IMAP or Pine.

Reinstall INBOX.new as INBOX:

+ Check to see if you have received any new messages while
            repairing INBOX.
          + If you haven't received any new messages while repairing
            INBOX, just rename INBOX.new to INBOX.
          + If you have received new messages, be sure to copy the new
            messages from INBOX to INBOX.new before doing the rename.

You now have a working INBOX, as well as two files with
          corrupted data (badmsg.1 and badmsg.2). There may be some
          useful data in the two badmsg files that you might want to try
          salvaging; otherwise you can delete the two badmsg files.
     _________________________________________________________________

7.16 What do the syslog messages:

imap/tcp server failing (looping)
 pop3/tcp server failing (looping)

mean? When it happens, the listed service shuts down. How can I fix
   this?

The error message "server failing (looping), service
          terminated" is not from either the IMAP or POP servers.
          Instead, it comes from inetd, the daemon which listens for TCP
          connections to a number of servers, including the IMAP and POP
          servers.

inetd has a limit of 40 new server sessions per minute for any
          particular service. If more than 40 sessions are initiated in a
          minute, inetd will issue the "failing (looping), service
          terminated" message and shut down the service for 10 minutes.
          inetd does this to prevent system resource consumption by a
          client which is spawning infinite numbers of servers. It should
          be noted that this is a denial of service; however for some
          systems the alternative is a crash which would be a worse
          denial of service!

For larger server systems, the limit of 40 is much too low. The
          limit was established many years ago when a system typically
          only ran a few dozen servers.

On some versions of inetd, such as the one distributed with
          most versions of Linux, you can modify the /etc/inetd.conf file
          to have a larger number of servers by appending a period
          followed by a number after the nowait word for the server
          entry. For example, if your existing /etc/inetd.conf line
          reads:

imap    stream  tcp     nowait  root    /usr/etc/imapd imapd

try changing it to be:

imap    stream  tcp     nowait.100  root    /usr/etc/imapd imapd

Another example (using TCP wrappers):

imap    stream  tcp     nowait  root    /usr/sbin/tcpd  imapd

try changing it to be:

imap    stream  tcp     nowait.100  root    /usr/sbin/tcpd  imapd

to increase the limit to 100 sessions/minute.

Before making this change, please read the information in "man
          inetd" to determine whether or not your inetd has this feature.
          If it does not, and you make this change, the likely outcome is
          that you will disable IMAP service entirely.

Another way to fix this problem is to edit the inetd.c source
          code (provided by your UNIX system vendor) to set higher
          limits, rebuild inetd, install the new binary, and reboot your
          system. This should only be done by a UNIX system expert. In
          the inetd.c source code, the limits TOOMANY (normally 40) is
          the maximum number of new server sessions permitted per minute,
          and RETRYTIME (normally 600) is the number of seconds inetd
          will shut down the server after it exceeds TOOMANY.
     _________________________________________________________________

7.17 What does the syslog message: Mailbox lock file /tmp/.600.1df3
   open failure: Permission denied mean?

This usually means that some "helpful" security script person
          has protected /tmp so that it is no longer world-writeable.
          /tmp must be world-writeable because lots of applications use
          it for scratch space. To fix this, do

chmod 1777 /tmp

as root.

If that isn't the answer, check the protection of the named
          file. If it is something other than 666, then either someone is
          hacking or some "helpful" person modified the code to have a
          different default lock file protection.
     _________________________________________________________________

7.18 What do the syslog messages:
 Command stream end of file, while reading line user=... host=...
 Command stream end of file, while reading char user=... host=...
 Command stream end of file, while writing text user=... host=...

mean?

This message occurs when the session is disconnected without a
          proper LOGOUT (IMAP) or QUIT (POP) command being received by
          the server first.

In many cases, this is perfectly normal; many client
          implementations are impolite and do this. Some programmers
          think this sort of rudeness is "more efficient".

The condition could, however, indicate a client or network
          connectivity problem. The server has no way of knowing whether
          there's a problem or just a rude client, so it issues this
          message instead of a Logout.

Certain inferior losing clients disconnect abruptly after a
          failed login, and instead of saying that the login failed, just
          say that they can't access the mailbox. They then complain to
          the system manager, who looks in the syslog and finds this
          message. Not very helpful, eh? See the answer to the Why can't
          I log in to the server? The user name and password are right!
          question.

If the user isn't reporting a problem, you can probably ignore
          this message.
     _________________________________________________________________

7.19 Why did my POP or IMAP session suddenly disconnect? The syslog
   has the message: Killed (lost mailbox lock) user=... host=...

This message only happens when either the traditional UNIX
          mailbox format or MMDF format is in use. This format only
          allows one session to have the mailbox open read/write at a
          time.

The servers assume that if a second session attempts to open
          the mailbox, that means that the first session is probably
          owned by an abandoned client. The common scenario here is a
          user who leaves his client running at the office, and then
          tries to read his mail from home. Through an internal mechanism
          called kiss of death, the second session requests the first
          session to kill itself. When the first session receives the
          "kiss of death", it issues the "Killed (lost mailbox lock)"
          syslog message and terminates. The second session then seizes
          read/write access, and becomes the new "first" session.

Certain poorly-designed clients routinely open multiple
          sessions to the same mailbox; the users of those clients tend
          to get this message a lot.

Another cause of this message is a background "check for new
          mail" task which does its work by opening a POP session to
          server every few seconds. They do this because POP doesn't have
          a way to announce new mail.

The solution to both situations is to replace the client with a
          good online IMAP client such as Pine. Life is too short to
          waste on POP clients and poorly-designed IMAP clients.
     _________________________________________________________________

7.20 Why does my IMAP client show all the files on the system,
   recursively from the UNIX root directory?
   7.21 Why does my IMAP client show all of my files, recursively from my
   UNIX home directory?

A well-written client should only show one level of hierarchy
          and then stop, awaiting explicit user action before going
          lower. However, some poorly-designed clients will recursively
          list all files, which may be a very long list (especially if
          you have symbolic links to directories that create a loop in
          the filesystem graph!).

This behavior has also been observed in some third-party
          c-client drivers, including maildir drivers. Consequently, this
          problem has even been observed in Pine. It is important to
          understand that this is not a problem in Pine or c-client; it
          is a problem in the third-party driver. A Pine built without
          that third-party driver will not have this problem.

See also the answer to Why does my IMAP client show all my
          files in my home directory?
     _________________________________________________________________

7.22 Why does my IMAP client show that I have mailboxes named
   "#mhinbox", "#mh", "#shared", "#ftp", "#news", and "#public"?

These are IMAP namespace names. They represent other
          hierarchies in which messages may exist. These hierarchies may
          not necessarily exist on a server, but the namespace name is
          still in the namespace list in order to mark it as reserved.

A few poorly-designed clients display all namespace names as if
          they were top-level mailboxes in a user's list of mailboxes,
          whether or not they actually exist. This is a flaw in those
          clients.
     _________________________________________________________________

7.23 Why does my IMAP client show all my files in my home directory?

As distributed, the IMAP server is connected to your home
          directory by default. It has no way of knowing what you might
          call "mail" as opposed to "some other file"; in fact, you can
          use IMAP to access any file.

Most clients have an option to configure your connected
          directory on the IMAP server. For example, in Pine you can
          specify this as the "Path" in your folder-collection, e.g.

Nickname  : Secondary Folders
 Server    : imap.example.com
 Path      : mail/
 View      :

In this example, the user is connected to the "mail"
          subdirectory of his home directory.

Other servers call this the "folder prefix" or similar term.

It is possible to modify the IMAP server so that all users are
          automatically connected to some other directory, e.g. a
          subdirectory of the user's home directory. Read the file CONFIG
          for more details.
     _________________________________________________________________

7.24 Why is there a long delay before I get connected to the IMAP or
   POP server, no matter what client I use?

There are two common occurances of this problem:

+ You are running a system (e.g. certain versions of Linux)
            which by default attempts to connect to an "IDENT" protocol
            (port 113) server on your client. However, a firewall or NAT
            box is blocking connections to that port, so the connection
            attempt times out.
            The IDENT protocol is a well-known bad idea that does not
            deliver any real security but causes incredible problems. The
            idea is that this will give the server a record of the user
            name, or at least what some program listening on port 113
            says is the user name. So, if somebody coming from port nnnnn
            on a system does something bad, IDENT may give you the userid
            of the bad guy.
            The problem is, IDENT is only meaningful on a timesharing
            system which has an administrator who is privileged and users
            who are not. It is of no value on a personal system which has
            no separate concept of "system administrator" vs.
            "unprivileged user".
            On either type of system, security-minded people either turn
            IDENT off or replace it with an IDENT server that lies. Among
            other things, IDENT gives spammers the ability to harvest
            email addresses from anyone who connects to a web page.
            This problem has been showing up quite frequently on systems
            which use xinetd instead of inetd. Look for files named
            /etc/xinetd.conf, /etc/xinetd.d/imapd, /etc/inetd.d/ipop2d,
            and /etc/xinetd.d/ipop3d. In those files, look for lines
            containing "USERID", e.g.
 log_on_success += USERID
            Hunt down such lines, and delete them ruthlessly from all
            files in which they occur. Don't be shy about it.
          + The DNS is taking a long time to do a reverse DNS (PTR
            record) lookup of the IP address of your client. This is a
            problem in your DNS, which either you or you ISP need to
            resolve. Ideally, the DNS should return the client's name;
            but if it can't it should at least return an error quickly.

As you may have noticed, neither of these are actual problems
          in the IMAP or POP servers; they are configuration issues with
          either your system or your network infrastructure. If this is
          all new to you, run (don't walk) to the nearest technical
          bookstore and get yourself a good pedagogical text on system
          administration for the type of system you are running.
     _________________________________________________________________

7.25 Why is there a long delay in Pine or any other c-client based
   application call before I get connected to the IMAP server? The hang
   seems to be in the c-client mail_open() call. I don't have this
   problem with any other IMAP client. There is no delay connecting to a
   POP3 or NNTP server with mail_open().

By default, the c-client library attempts to make a connection
          through rsh (and ssh, if you enable that). If the command:

rsh imapserver exec /etc/rimapd

(or ssh if that is enabled) returns with a "* PREAUTH"
          response, it will use the resulting rsh session as the IMAP
          session and not require an authentication step on the server.

Unfortunately, rsh has a design error that treats "TCP
          connection refused" as "temporary failure, try again"; it
          expects the "rsh not allowed" case to be implemented as a
          successful connection followed by an error message and close
          the connection.

It must be emphasized that this is a bug in rsh. It is not a
          bug in the IMAP toolkit.

The use of rsh can be disabled in any the following ways:

+ You can disable it for this particular session by either:
               o setting an explicit port number in the mailbox name,
                 e.g.
 {imapserver.foo.com:143}INBOX
               o using SSL (the /ssl switch)
          + You can disable rsh globally by setting the rsh timeout value
            to 0 with the call:
 mail_parameters (NIL,SET_RSHTIMEOUT,0);
     _________________________________________________________________

7.26 Why does a message sometimes get split into two or more messages
   on my SUN system?

This is caused by an interaction of two independent design
          problems in SUN mail software. The first problem is that the
          "forward message" option in SUN's mail tool program includes
          the internal "From " header line in the text that it forwarded.
          This internal header line is specific to traditional UNIX
          mailbox files and is not suitable for use in forwarded
          messages.

The second problem is that the mail delivery agent assumes that
          mail reading programs will not use the traditional UNIX mailbox
          format but instead an incompatible variant that depends upon a
          Content-Length: message header. Content-Length is widely
          recognized to have been a terrible mistake, and is no longer
          recommended for use in mail (it is used in other facilities
          that use MIME).

One symptom of the problem is that under certain circumstances,
          a message may get broken up into several messages. I'm also
          aware of security bugs caused by programs that foolishly trust
          "Content-Length:" headers with evil values.

To fix the mailer on your system, edit your sendmail.cf to
          change the Mlocal line to have the -E flag. A typical entry
          will lool like:

Mlocal,        P=/usr/lib/mail.local, F=flsSDFMmnPE, S=10, R=20,
                A=mail.local -d $u

This fix will also work around the problem with mail tool,
          because it will insert a ">" before the internal header line to
          prevent it from being interpreted by mail reading software as
          an internal header line.
     _________________________________________________________________

7.27 Why did my POP or IMAP session suddenly disconnect? The syslog
   has the message:
 Autologout user=<...my user name...> host=<...my client system...>

This is a problem in your client.

In the case of IMAP, it failed to communicate with the IMAP
          server for over 30 minutes; in the case of POP, it failed to
          communicate with the POP server for over 10 minutes.
     _________________________________________________________________

7.28 What does the UNIX error message: TLS/SSL failure: myserver: SSL
   negotiation failed mean?
   7.29 What does the PC error message: TLS/SSL failure: myserver:
   Unexpected TCP input disconnect mean?

This usually means that an attempt to negotiate TLS encryption
          via the STARTTLS command failed, because the server advertises
          STARTTLS functionality, but doesn't actually have it (e.g.
          because no certificates are installed).

Use the /notls option in the mailbox name to disable TLS
          negotiation.
     _________________________________________________________________

7.30 What does the error message: TLS/SSL failure: myserver: Server
   name does not match certificate mean?

An SSL or TLS session encryption failed because the server name
          in the server's certificate does not match the name that you
          gave it. This could indicate that the server is not really the
          system you think that it is, but can be also be called if you
          gave a nickname for the server or name that was not
          fully-qualified. You must use the fully-qualified domain name
          for the server in order to validate its certificate

Use the /novalidate-cert option in the mailbox name to disable
          validation of the certificate.
     _________________________________________________________________

7.31 What does the UNIX error message: TLS/SSL failure: myserver:
   self-signed certificate mean?
   7.32 What does the PC error message: TLS/SSL failure: myserver:
   Self-signed certificate or untrusted authority mean?

An SSL or TLS session encryption failed because your server's
          certificate is "self-signed"; that is, it is not signed by any
          Certificate Authority (CA) and thus can not be validated. A
          CA-signed certificate costs money, and some smaller sites
          either don't want to pay for it or haven't gotten one yet. The
          bad part about this is that this means there is no guarantee
          that the server is really the system you think that it is.

Use the /novalidate-cert option in the mailbox name to disable
          validation of the certificate.
     _________________________________________________________________

7.33 What does the UNIX error message: TLS/SSL failure: myserver:
   unable to get local issuer certificate mean?

An SSL or TLS session encryption failed because your system
          does not have the Certificate Authority (CA) certificates
          installed on OpenSSL's certificates directory. On most systems,
          this directory is /usr/local/ssl/certs). As a result, it is not
          possible to validate the server's certificate.

If CA certificates are properly installed, you should see
          factory.pem and about a dozen other .pem names such as
          thawteCb.pem.

As a workaround, you can use the /novalidate-cert option in the
          mailbox name to disable validation of the certificate; however,
          note that you are then vulnerable to various security attacks
          by bad guys.

The correct fix is to copy all the files from the certs/
          directory in the OpenSSL distribution to the
          /usr/local/ssl/certs (or whatever) directory. Note that you
          need to do this after building OpenSSL, because the OpenSSL
          build creates a number of needed symbolic links. For some
          bizarre reason, the OpenSSL "make install" doesn't do this for
          you, so you must do it manually.
     _________________________________________________________________

7.34 Why does reading certain messages hang when using Netscape? It
   works fine with Pine!

There are two possible causes.

Check the mail syslog. If you see the message "Killed (lost
          mailbox lock)" for the impacted user(s), read the FAQ entry
          regarding that message.

Check the affected mailbox to see if there are embedded NUL
          characters in the message. NULs in message texts are a
          technical violation of both the message format and IMAP
          specifications. Most clients don't care, but apparently
          Netscape does.

You can work around this by rebuilding imapd with the
          NETSCAPE_BRAIN_DAMAGE option set (see src/imapd/Makefile); this
          will cause imapd to convert all NULs to 0x80 characters. A
          better solution is to enable the feature in your MTA to
          MIME-convert messages with binary content. See the
          documentation for your MTA for how to do this.
     _________________________________________________________________

7.35 Why does Netscape say that there's a problem with the IMAP server
   and that I should "Contact your mail server administrator."?

Certain versions of Netscape do this when you click the Manage
          Mail button, which uses an undocumented feature of Netscape's
          proprietary IMAP server.

You can work around this by rebuilding imapd with the
          NETSCAPE_BRAIN_DAMAGE option set (see src/imapd/Makefile) to a
          URL that points either to an alternative IMAP client (e.g.
          Pine) or perhaps to a homebrew mail account management page.
     _________________________________________________________________

7.36 Why is one user creating huge numbers of IMAP or POP server
   sessions?

The user is probably using Outlook Express, Eudora, or a
          similar program. See the answer to the Help! My load average is
          soaring and I see hundreds of POP and IMAP servers, many logged
          in as the same user! question.
     _________________________________________________________________

7.37 Why don't I get any new mail notifications from Outlook Express
   or Outlook after a while?

This is a known bug in Outlook Express. Microsoft is aware of
          the problem and its cause. They have informed us that they do
          not have any plans to fix it at the present time.

The problem is also reported in Outlook 2000, but not verified.

Outlook Express uses the IMAP IDLE command to avoid having to
          "ping" the server every few minutes for new mail.
          Unfortunately, Outlook Express overlooks the part in the IDLE
          specification which requires that a client terminate and
          restart the IDLE before the IMAP 30 minute inactivity
          autologout timer triggers.

When this happens, Outlook Express displays "Not connected" at
          the bottom of the window. Since it's no longer connected to the
          IMAP server, it isn't going to notice any new mail.

As soon as the user does anything that would cause an IMAP
          operation, Outlook Express will reconnect and new mail will
          flow again. If the user does something that causes an IMAP
          operation at least every 29 minutes, the problem won't happen.

Modern versions of imapd attempt to work around the problem by
          automatically reporting fake new mail after 29 minutes. This
          causes Outlook Express to exit the IDLE state; as soon as this
          happens imapd revokes the fake new mail. As long as this
          behavior isn't known to cause problems with other clients, this
          workaround will remain in imapd.
     _________________________________________________________________

7.38 Why don't I get any new mail notifications from Entourage?

This is a known bug in Entourage.

You built an older version of imapd with the
          MICROSOFT_BRAIN_DAMAGE option set, in order to disable support
          for the IDLE command. However, Entourage won't get new mail
          unless IDLE command support exists.

Note: the MICROSOFT_BRAIN_DAMAGE option no longer exists in
          modern versions, as the Outlook Express problem which it
          attempted to solve has been worked around in another way.
     _________________________________________________________________

7.39 Why doesn't Entourage work at all?

It's hard to know. Entourage breaks almost every rule in the
          book for IMAP. It is highly instructive to do a packet trace on
          Entourage, as an example of how not to use IMAP. It does things
          like STATUS (MESSAGES) on the currently selected mailbox and
          re-fetching the same static data over and over again.

It seems that every time we understand what it is doing wrong
          in Entourage and come up with a workaround, we learn about
          something else that's broken.

Try building imapd with the ENTOURAGE_BRAIN_DAMAGE option set,
          in order to disable the diagnostic that occurs when doing
          STATUS on the currently selected mailbox.
     _________________________________________________________________

7.40 Why doesn't Netscape Notify (NSNOTIFY.EXE) work at all?

This is a bug in NSNOTIFY; it doesn't handle unsolicited data
          from the server correctly.

Fortunately, there is no reason to use this program with IMAP;
          NSNOTIFY is a polling program to let you know when new mail has
          appeared in your maildrop. This is necessary with POP; but
          since IMAP dynamically announces new mail in the session you're
          better off (and will actually cause less load on the server!)
          keeping your mail reading program's IMAP session open and let
          IMAP do the notifying for you.

Consequently, the recommended fix for the NSNOTIFY problem is
          to delete the NSNOTIFY binary.
     _________________________________________________________________

7.41 Why can't I connect via SSL to Eudora? It says the connection has
   been broken, and in the server syslogs I see "Command stream end of
   file".

There is a report that you can fix the problem by going into
          Eudora's advanced network configuration menu and increasing the
          network buffer size to 8192.
     _________________________________________________________________

7.42 Sheesh. Aren't there any good IMAP clients out there?

Yes!

Pine is a wonderful client. It's fast, it uses IMAP well, and
          it generates text mail (life is too short to waste on HTML
          mail). Also, there are some really wonderful things in progress
          in the Pine world.

There are some good GUI clients out there, mostly from smaller
          vendors. Without naming names, look for the vendors who are
          active in the IMAP protocol development community, and their
          products.

Netscape, Eudora, and Outlook can be configured with enough
          effort to be good citizens and work well for users, but they
          can also be badly misconfigured, and often the misconfiguration
          is the default.
     _________________________________________________________________

7.43 But wait! PC Pine (or other PC program build with c-client)
   crashes with the message incomplete SecBuffer exceeds maximum buffer
   size when I use SSL connections. This is a bug in c-client, right?

It's a bug in the Microsoft SChannel.DLL, which implements SSL.
          Microsoft admits it (albeit with an unstatement: "it's not
          fully RFC compliant"). The problem is that SChannel indicates
          that the maximum SSL packet data size is 5 bytes smaller than
          the actual maximum. Thus, any IMAP server which transmits a
          maximum sized SSL packet will not work with PC Pine or any
          other program which uses SChannel.

It can take a while for the problem to show up. The client has
          to do something that causes at least 16K of contiguous data.
          Many clients do partial fetching, which tends to reduce the
          number of cases where this can happen. However, all software
          which uses SChannel to support SSL is affected by this bug.

This problem does not affect UNIX code, since OpenSSL is used
          on UNIX.

This problem most recently showed up with the CommunigatePro
          IMAP server. They have an update which trims down their maximum
          contiguous data to less than 16K, in order to work around the
          problem.

This problem has also shown up with the Exchange IMAP server
          with UNIX clients (including Pine built with an older version
          of c-client) which sends full-sized 16K SSL packets. Modern
          c-client works around the problem by trimming down its maximum
          outgoing SSL packet size to 8K.

Microsoft has developed a hotfix for this bug. Look up MSKB
          article number 300562. Contrary to the article text which
          implies that this is a Pine issue, this bug also affect
          Microsoft Exchange server with *any* UNIX based client that
          transmits full-sized SSL payloads.
     _________________________________________________________________

7.44 My qpopper users keep on getting the DON'T DELETE THIS MESSAGE --
   FOLDER INTERNAL DATA if they also use Pine or IMAP. How can I fix
   this?

This is an incompatibility between qpopper and the c-client
          library used by Pine, imapd, and ipop[23]d.

Assuming that you want to continue using qpopper, look into
          qpopper's --enable-uw-kludge-flag configuration flag, which is
          documented as "check for and hide UW 'Folder Internal Data'
          messages".

The other alternative is to switch from qpopper to ipop3d.
     _________________________________________________________________

7.45 Help! I installed the servers but I can't connect to them from my
   client!

Review the installation instructions carefully. Make sure that
          you have not skipped any of the steps. Make sure that you have
          made the correct entries in the configuration files; pay
          careful attention to the exact spelling of the service names
          and the path names. Make sure as well that you have properly
          restarted inetd.

If you have a system with Yellow Pages/NIS such as Solaris,
          have you updated the service names there as well as in
          /etc/services?

If you have a system with TCP wrappers, have you properly
          updated the TCP wrapper files (e.g. /etc/hosts.allow and
          /etc/hosts.deny) for the servers?

If you have a system which uses xinetd instead of inetd, have
          you made sure that you have made the correct corresponding
          xinetd changes for those services?

Try telneting to the server port (143 for IMAP, 110 for POP3).
          If you get a "refused" error, that probably means that you
          don't have the service set up in inetd.conf. If the connection
          opens and then closes with no message, the service is set up,
          but either the path name of the server binary in inetd.conf is
          wrong or your TCP wrappers are configured to deny access.

If you don't know how to make the corresponding changes to
          these files, seek the help of a local expert for your system.
     _________________________________________________________________

7.46 Why do I get the message Can not authenticate to SMTP server: 421
   SMTP connection went away! and why did this happen? There was also
   something about SECURITY PROBLEM: insecure server advertised
   AUTH=PLAIN

Some versions of qmail, including that running on
          mail.smtp.yahoo.com, disconnect the SMTP session if you fail to
          authenticate prior to attempting to transmit mail. An attempt
          to authenticate was made, but it failed because the server had
          already disconnected.

To work around this, you need to specify /user=... in the host
          name specification.

The SECURITY PROBLEM came about because the server advertised
          the AUTH=PLAIN SASL authentication mechanism outside of a
          TLS-encrypted session, in violation of RFC 4616. This message
          is just a warning, and in fact occurred after the server had
          disconnected.
     _________________________________________________________________

7.47 Why do I get the message SMTP Authentication cancelled and why
   did this happen? There was also something about SECURITY PROBLEM:
   insecure server advertised AUTH=PLAIN

This is a bug in the SMTP server.

Some versions of qmail, including that running on
          mail.smtp.yahoo.com, have a bug in their implementation of SASL
          in their SMTP server, which renders it non-compliant with the
          standard.

If the client does not provide an initial response in the
          command line for an authentication mechanism whose profile does
          not have an initial challenge, qmail issues a bogus response:

334 ok, go on

The problem is the "ok, go on". This violates RFC 4954's
          requirement that the text part in a 334 response be a BASE64
          encoded string; in other words, it is a protocol syntax error.

In the case of AUTH=PLAIN, RFC 4422 (page 7) requires that the
          encoded string have no data. In other words, the appropropiate
          standards-compliant server response is "334" followed by a
          SPACE and a CRLF.

The SECURITY PROBLEM came about because the server advertised
          the AUTH=PLAIN SASL authentication mechanism outside of a
          TLS-encrypted session, in violation of RFC 4616. This message
          is just a warning, and is not related the "Authentication
          cancelled" problem.
     _________________________________________________________________

7.48 Why do I get the message Invalid base64 string when I try to
   authenticate to a Cyrus server?

This slightly misleading message is the way that a Cyrus server
          indicates that an authentication exchange was cancelled. It is
          not indicative of a bug or protocol violation.

The most common reason that this happens is if the Cyrus server
          offers Kerberos authentication, c-client is built with Kerberos
          support, but your client system is not within the Kerberos
          realm. In this case, the client code will try to authenticate
          via Kerberos, fail to get the Kerberos credentials, cancel the
          authentication attempt, and try the next available
          authentication technology.
     _________________________________________________________________

8. Where to Go For Additional Information
     _________________________________________________________________

8.1 Where can I go to ask questions?
   8.2 I have some ideas for enhancements to IMAP. Where should I go?

If you have questions about the IMAP protocol, or want to
          participate in discussions of future directions of the IMAP
          protocol, the appropriate mailing list is
          imap-protocol@u.washington.edu. You can subscribe to this
          list via imap-protocol-request@u.washington.edu

If you have questions about this software, you can send me
          email directly or use the imap-uw@u.washington.edu mailing
          list. You can subscribe to this list via
          imap-uw-request@u.washington.edu

If you have general questions about the use of IMAP software
          (not specific to the UW IMAP toolkit) use the
          imap-use@u.washington.edu mailing list. You can subscribe to
          this list via imap-use-request@u.washington.edu

You must be a subscriber to post to these lists.  As an
          alternative, you can use the comp.mail.imap newsgroup.
          _________________________________________________________________

8.3 Where can I read more about IMAP and other email protocols?

We recommend Internet Email Protocols: A Developer's Guide, by
          Kevin Johnson, published by Addison Wesley, ISBN 0-201-43288-9.
     _________________________________________________________________

8.4 Where can I find out more about setting up and administering an
   IMAP server?

We recommend Managing IMAP, by Dianna Mullet & Kevin Mullet,
          published by O'Reilly, ISBN 0-596-00012-X.

This book also has an excellent comparison of the UW and Cyrus
          IMAP servers.

Last Updated: 15 November 2007

MR SKB