gnul put forth on 1/20/2010 3:41 PM:
My favorite feature of Dovecot is the full-text indexing of messages. I love searching through message bodies of thousands of messages (using RoundCube or Thunderbird) in amazingly short periods of time.
I'll second that. I use Dovecot with mbox format. I've got one IMAP folder (mbox file) with 10,800 list mail messages in it, file is about 45MB. The longest body search time I've seen was about 10 seconds. The server is an old dual 550 box with 384MB RAM and a single 500GB SATA disk runny Debian Lenny. This is a vanity server so it's very lightly loaded, but the search times are still pretty impressive given the age/performance of the hardware.