Dovecot is a good server. It is one of only two (the other being Panda
IMAP) that fully passes IMAP compliance testing:
http://imapwiki.org/ImapTest/ServerStatus
[UW IMAP flunks two of the tests...it hasn't been updated in 2 years.]
The main concern that I have with using Dovecot for traditional UNIX
mailbox files ("mbox") is that Dovecot gives up some of the aggressive
compatibility with ancient/stupid mbox practices for performance.
UW (and Panda) try damn hard to be compatible with even the most ancient
stupid things that people do with mbox files; and take a considerable
performance hit for doing so.
UW and Panda assume the worst about mbox. It assumes that NFS is probably
in the picture, that you may well be farting around in some ancient 1980s
mbox tool at the same time that the IMAP server is trying to do something;
and thus it has to go through extreme checks to make sure that your mbox
file doesn't get trashed.
This aggressive support for worst case was there for a reason. That worst
case actually existed once upon a time. I hope that it is forever
extinct, but people tend to do crazy things... Oh well, mankind will
probably survive even though it refuses to take my advice... :)
The issues to be aware of in Dovecot are:
[1] Access to the mbox files via NFS; a true idiocy but nonetheless one
that UW itself insisted upon doing for years (over my repeated and
vigorous objections). I don't think that Dovecot tries to make an NFS
back end work right. I wouldn't blame him for not doing so; most of the
UW IMAP performance slowdown with mbox files is code to make NFS work (for
a half-assed "sort of" definition of "work").
[2] Dovecot runs multi-threaded (which itself requires OS support), and
the threads exchange state information. Among other things, this allows
significant performance benefits and multiple read-write access to the
same mbox format mailbox...as long as Dovecot is the only consumer of the
mbox file. Once again, UW IMAP did not have the luxury of being able to
assume that.
The nice thing about mix format is that there was no need to be compatible
with ancient idiocies; and as a result mix is so much faster. Even
without the threading, mix is probably faster than Dovecot on mbox because
even Dovecot has to do some mbox operations the hard way.
Nonetheless, if you really need mbox format, and are sure that you won't
be running dinoware and/or doing stupid things like access via NFS, then
Dovecot is definitely an option to consuder.
If you want to use maildir format, I would go further and say that Dovecot
is the ONLY choice; do not use an unsupported third-party driver in UW and
especially do not use Courier.
-- Mark --
http://panda.com/mrc
Democracy is two wolves and a sheep deciding what to eat for lunch.
Liberty is a well-armed sheep contesting the vote.
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