What directory names does Dovecot use to name mailboxes?

Question

Over the New Years' weekend I migrated our mail server from a PPC-based Xserve G4 running OS X Server 10.5.8 to a new Intel Mac Mini running OS X Server 10.6.5. Overall, the migration was fairly straightforward, but we did have a mail glitch. Apple’s migration script run by Server Assistant (System/Library/ServerSetup/MigrationExtras/65mailmigrator.pl) created mailboxes at /var/spool/imap/dovecot/mail, as it should, but named the folders containing the migrated mail according to actual user names: like “bert” and “joe” and so on. When we actually fired up the mail server and watched what happened as new mail arrived or users logged in via POP / IMAP, we discovered that Dovecot was creating mail folders in /var/spool/imap/dovecot/mail named according to the users' GUIDs, such as A7FC2F6C-86C3-4119-B9C9-58B9B60E2066. So an entirely new set of mailboxes was being created, and the migrated mail wasn’t seen by our users at all.
Which is correct? Should the Dovecot mailboxes be named according to GUIDs or user names? We’re puzzled by the fact that Apple’s migration script created folders based on the users name whereas Dovecot appears to want to create folders based on GUID. I was able to manually copy over the contents of the migrated mail (bert/cur/*, joe/cur/*, and so on) to their proper locations, initially by hand for two users and then I wrote a small script to automate the copy for the remaining mailboxes. As a result, everyone received their migrated mail, though somewhat delayed and in some cases appearing more than once in their InBox as a result.
Our mail server, both in Leopard and SL form, is an Open Directory replica slaved off an Open Directory master. We had some fairly major corruptions present in the Leopard Server-based OD database we’d been using, so I made the decision to manually rekey a fresh OD database in from scratch using Workgroup Manager. I preserved user’s long and short names, UIDs, and group memberships but of course this new OD database had entirely new GUIDs for users. At first I thought the reason that Dovecot was using GUIDs to identify users it might have to do with the fact that the OD database had been rekeyed, and all the GUIDs had changed. Since then, however, I’ve brought up an experimental SL Server, also an OD replica of the same master. After enabling mail service on the experimental SL Server I’m seeing that Dovecot is also creating folders named by GUIDs as new mail arrives, and this server never knew what the original Leopard GUIDs were, so I must assume this is normal behavior.
…so the bottom line is which is correct: GUIDs or user names for Dovecot's mailboxes at /var/spool/imap/dovecot/mail? Assuming the answer is GUIDs then I have a bit of cleanup to delete all the folders that Dovecot isn’t using: right now it’s a bit of a mess. If it is supposed to be GUIDs, then the next question is why did Apple‘s migration script create folders based on user names and not GUIDs?
…Any help would be appreciated.

Answer 1

R Bryan Harrison mentioned that Dovecot on his SL Servers name directories within /var/imap/dovecot/mail with GUIDs, not user names, as I noticed on a test server I built (a sandbox server). So it looks like our production mail system is doing the right thing.