I’m looking into IMAP server software as an upgrade to an existing server that is running an old version of Cyrus.
This article was also somewhat influential in my evaluation of different options. I had no idea how politicized the history of IMAP has been. I had some prior bad experiences with file locking and UW IMAP due to use of the mbox format–users would forget and leave their e-mail client open on their home computer, then strange things would happen when they tried to access their e-mail at work because the files were already locked by the other e-mail client. I have also had nightmares with Cyrus and Berkeley DB.
In the end, I decided to go with RavenCore due to its philosophy of trying to use the OS‘s own built-in tools and Perl as the underlying scripting language. As a bonus, it has a nice interface for managing hosted websites as well, so we can use this same interface on our new web server when we roll it out later this year. I have been using RavenCore for a few months now and it does a very nice job of integrating Amavis, Clamav, SpamAssassin, SquirrelMail, BIND DNS administration, pretty much everything that I wanted and needed to use.