Cyrus IMAP Server FAQ

Cyrus IMAP Server FAQ

  • POP-Before-SMTP It is not included in the default distribution because there is already a standard way of doing this with SMTP AUTH. Any good MTA and/or MUA should support SMTP AUTH, so we shouldn't have to create a hack in an unrelated service. However, if you would like to install it anyway, we recommend using DRAC, along with the patch available in contrib/drac_auth.patch.
  • Using NFS We don't recommend it. If you want to do it, it may possibly work but you may also lose your email or have corrupted cyrus.* files. You can look at the mailing list archives for more information.
  • Using AFS/Coda We don't recommend it. It's even less likely to work than NFS. If you want to do it, it may possibly work but you may also lose your email or have corrupted cyrus.* files. CMU's previous e-mail system, AMS, leveraged AFS extensively for storage (and transit) purposes. For various reasons it didn't scale particularly well and led to CMU's interest in IMAP.

    Cyrus was designed to use a local filesystem with Unix semantics and a working mmap()/write() combination. AFS doesn't provide these semantics so won't work correctly.

  • Virtual hosting - See virtual domains configuration.
  • dots in userids - you can have a '.' in your username IF, AND ONLY IF, you use the UNIX hierarchy convention.
  • renaming users - Supported, but try to make sure that the user is not, and cannot login when doing the rename. Otherwise user-meta may get corrupted and/or out of sync.
  • plus addressing - Plus addressing allows direct delivery to a particular mailbox (other than an INBOX). This is done in two ways.

    The first way allows delivery to a subfolder of a specific user's INBOX. This is done via an address of the form: username+mailfolder@domain, which will deliver to the user's INBOX.mailfolder folder (or altnamespace equivalent). This submailbox must allow the posting user the 'p' right (generally, this means 'anyone' must have the 'p' right), otherwise the message will just be filed into the user's INBOX.

    The second way is to form an address like [postuser]+mailfolder@domain. This will deliver into the mailbox 'mailfolder'. [postuser] is the string specified in the imapd.conf option of the same name, and may be the empty string. As before, the posting user will need to have the 'p' right on the mailbox.

    For both methods, if 'mailfolder' is more than one level deep, you will need to conform to the hierarchy separator appropriate to your site.

  • Performance/Capacity/Scaling - See the performance guide.

General Questions

Q: What are the advantages of LMTP?

A: LMTP protocol differs from SMTP in that it causes the Cyrus to return, after the final "." of the DATA command, one reply for each recipient. If, for example, a server is given a transaction for two recipients, delivery to the first succeeds, and delivery to the second encounters a temporary failure condition, the MTA will get a separate response for each recipient and will only have to reattempt to deliver it to the second recipient. If using SMTP, only a single temporary failure response would be returned, and the entire transaction would have to be reattempted.

Furthermore, LMTP is superior to invoking command-line delivery agents from the MTA in that most ESMTP extensions are supported by LMTP, without having to extend any interfaces.

Lastly, because LMTP can be run over TCP, it allows you to run SMTP (and spam/virus scanning) and mailbox access on separate servers, thus allowing better scalability.

Q: How do I configure my MTA?

A: See Configuring the Mail Transfer Agent

Q: How should I configure partitions to deal with a large number of users?

A: The key is not to over-subscribe any partitions. Avoid putting too many users on any one partition, such that read/write performance becomes unacceptable. Good RAID performance (plenty of read/write cache, and perhaps RAID 10 instead of RAID 5) will improve the number of users a partition can serve. To benefit from multiple partitions, each should be on its own set of disks, served by an unsaturated interface (FC, SCSI, SAS, SATA, etc) to the host running Cyrus.

See the performance guide or general performance guidelines. Also see metapartition_files and metapartition-name in imapd.conf.5 for additional configuration options which can help with performance, especially if you have access to high-speed storage (faster than disks).

Troubleshooting

Q: Why doesn't imapd/pop3d/nntpd/lmtpd/timsieved advertise PLAIN or plaintext login commands?

A: Unless otherwise configured, Cyrus services only advertise PLAIN or plaintext login commands on encrypted connections (SSL-wrapped connections or after a successful STARTTLS command). This behavior can be changed with the use of the allowplaintext option in imapd.conf.5.

Q: I'm getting syslog'd messages from the master process saying processes are "signaled to death by 10". What's up?

A: If you're using Berkeley DB 3.0.55, try installing some patches to Berkeley DB available from http://www.sleepycat.com/update/3.0.55/patch.3.0.55.html.

Q: I've used saslpasswd2 to create CRAM-MD5 secrets, but imapd doesn't say AUTH=CRAM-MD5. Why?

A: Make sure /etc/sasldb2 is readable by the Cyrus user.

Q: I'm using "sasl_pwcheck_method: saslauthd", but authentication isn't working.

A: Make sure that the saslauthd daemon is running (you'll want to start it when the system boots). imapd is unable to connect to saslauthd if the following message appears in the logs:

Dec  6 12:58:57 mail3.andrew.cmu.edu imapd[1297]: cannot connect to saslauthd server

Make sure that saslauthd is running and that the cyrus user can access the unix domain socket (defaults to /var/run/mux).

Q: I'm getting messages about "duplicate_prune". What's wrong?

A: These messages look like

Jan 14 13:46:24 grant ctl_deliver[9060]: duplicate_prune: opening
  /var/imap/deliverdb/deliver-x.db: No such file or directory
Jan 14 13:46:24 grant ctl_deliver[9060]: duplicate_prune: opening
  /var/imap/deliverdb/deliver-y.db: No such file or directory
Jan 14 13:46:24 grant ctl_deliver[9060]: duplicate_prune: opening
  /var/imap/deliverdb/deliver-z.db: No such file or directory

These messages are normal; one file is maintained for each user beginning with "x", "y", "z", etc. If you're first starting or you have no users beginning with these letters, these messages are completely normal and can be ignored.

Q: I'm getting a message about "imapd: could not getenv(CYRUS_SERVICE); exiting" in my imapd.log. What's wrong?

A: Remove all imap, pop, lmtp and sieve lines from [x]inetd.conf and restart [x]inetd. Cyrus is run out of its own "master" process.

Q: How do I use different SSL/TLS certificates for imap and pop?

A: Specify the different certs using the appropriate options in imapd.conf. Read imapd.conf(5) for details.

Q: My KPOP client is complaining about TLS keys. What should I do?

A: Disable TLS for the kpop service. Either set tls_pop3_cert_file to disabled in imapd.conf (which will also disable SSL/TLS for pop3), or use a separate config file for kpop. For example, change the kpop service in cyrus.conf to something like:

kpop    cmd="pop3d -k -C /etc/kpopd.conf" listen="kpop"

then copy /etc/imapd.conf to /etc/kpopd.conf and remove the tls_* options.

Q: Eudora 5.x can't connect using STARTTLS ("SSL Neogotiation Failed"). What should I do?

A: First, complain to QUALCOMM because their STARTTLS implementation is broken. Eudora doesn't support TLSv1 (per RFC2246) and Cyrus requires it. If you really need this before it is fixed in Eudora, remove or comment out the following lines in tls.c:

    if (tlsonly) {
        off |= SSL_OP_NO_SSLv2;
        off |= SSL_OP_NO_SSLv3;
    }
Q: I'm getting messages in imapd.log like:
Sep 11 17:23:55 ogg lmtpd[773]: DBERROR db3: 16 lockers
Sep 11 17:23:55 ogg lmtpd[1409]: DBERROR db3: 17 lockers
Sep 11 17:23:56 ogg lmtpd[1508]: DBERROR db3: 9 lockers
Sep 11 17:23:56 ogg lmtpd[776]: DBERROR db3: 9 lockers
What's wrong?

A: Nothing is wrong. These messages are logged whenever Berkeley DB encounters lock contention, but aren't necessarily problems. This is especially likely when you have an empty or small duplicate delivery database and are receiving a large volume of e-mail.

Berkeley DB 4.0 has a bug where the number of lockers isn't decremented properly, causing this number to be unreliable.

Q: All of the 8bit characters in the headers of messages that I receive are being changed to 'X's. What's going on?

A: 8-bit characters are illegal in message headers. Following the principle of "be liberal in what you accept, and strict in what you send", Cyrus converts them to Xs. (Without a character set, having the 8-bit characters replaced with Xs is just as good as having them be any other 8-bit character, especially for sorting and searching). Alternatively, you can set "reject8bit: t" in imapd.conf to reject the messages outright. It might also be reasonable for Cyrus to support the use of a default character set, however thus far no one has done the work to do so (it would also involve QP-encoding the corrupted headers).

Q: Why can't I delete any messages from my over-quota mailbox? I'm using a client with a 'trash folder'.

A: Trash folders, as they are commonly implemented (as actual IMAP mailboxes), do not fit the IMAP delete/expunge model very well. In fact, naive client implementations will get stuck in a situation where they cannot delete a message from a mailbox because they try to COPY it to the trash folder before deleting the message. This operation will fail due to the mailbox being over quota. This is separate from the fact that a specific mailbox name is not interoperable between clients (one might call it 'trash', another 'Trash', another 'Recycle Bin', etc)

Given the lack of protocol support for a trash folder, this is mostly a quality-of-implementation issue on the client side. There are a few options here:

  • Contact your client vendor to have the broken client fixed (one possibility is to have the client ask the user if they wish to permanantly delete the message if the COPY operation fails).
  • Stop using the 'trash mailbox' feature of your client (if possible).
  • Set a separate quota root on the 'trash folders' of users. This last option is significantly harder to do correctly, since it assumes that all clients that make use of a trash folder do so with the same folder name.

Q: How do I stop Cyrus from advertising the DIGEST-MD5 and CRAM-MD5 shared secret SASL mechanisms?

A: Not really a Cyrus IMAPd question, this can be fixed by just removing the SASL plugins from where Cyrus SASL installed them (if no other applications require them), or by using the sasl_mech_list imapd.conf option to list only the mechanisms that you require.


last modified: $Date: 2010/01/06 17:01:29 $
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