I finally got my aging FC2 box retired and moved all email to my new CentOS 5 box. My site is all-IMAP, no POP3.
I have one user who downloads all email to Thunderbird on his laptop so that he can work offline while away from a network connection (eg. on an airplane). I forgot to change the pop3_uidl_format setting as described here:
http://wiki.dovecot.org/Upgrading/1.0
So he was seeing repeated downloads of all his mail (about 300 MBytes) every time he connected. (I'm not sure why it didn't happen only the first time.) I changed the setting and haven't heard back whether if fixed things for him.
Does this setting in fact get used by IMAP? It's in the POP3 section, so I'm wondering if it takes effect when one is using IMAP from the client.
CentOS 5 is currently shipping with:
dovecot-1.0-1.2.rc15.el5
I may look for a newer release. CentOS, based on RHEL, is intended to be a conservative distro, so I'll probably need to look at RPMForge (an addon repository of more exotic and bleeding edge software) to see if it offers a newer release.