I am attempting to test out dovecot on a server on a separate IP address from the live, functioning UW-IMAP. I am having mixed results with dovecot. An entirely new account that's never been used with UW-IMAP seems to work fine, but that's really not the point of the exercise.
If I try changing over an existing account to use dovecot, I get a variety of issues. Testing with Apple Mail.app, if I synchronize the account, the INBOX stops displaying. So off to plan B, and debug via command line commands.
I tried connecting to Dovecot. It was able to list the mailboxes for me. I asked for status on INBOX. Sometimes I get an error back in the IMAP stream, sometimes not. Either way, the log shows complaints about creating mail/.imap and below (we use mbox format, plus /var/mail/%u for inbox).
I have active namespace compatibility recommended by the Wiki so that clients specifying "mail/" and clients not specifying an imap path both work. With the test account, I proved this functionality is working.
At this point I clearly have some issues, and could use some help figuring out what to ask for help with, i.e. how to proceed to debug this without damaging the existing UW-IMAP setup in the process. The goal is to cut over to dovecot once I can be sure it really is working compatibly, but until then I have a large user base and can't blow everything up.
And yes, I really, truly have RTFM (i.e. read the Wiki, the troubleshooting pages, the migration pages).