Having some trouble with poor performance with UW IMAP server finally pushed me over the edge today, so I migrated to Dovecot. A good move. Took me a while to figure out that I needed to turn OFF the namespace setting in my mail client (Mozilla, Thunderbird) in “Server Settings -> Advanced”. I also had to make the default mail dir ~/.maildir/.
This great Perl script eased the conversion of old mbox format to new maildir format.