[Dovecot] user_db, uid/gid and maildir

[vmstech]

Im experimenting with putting all my virtual users mail under 1
directory with belonging to a system user created for the purpose. The
mode on the directory (and subdirectories) is 770.

I keep all my virtual users details in a postgres database.

My interpretation of the wiki documentation is that if the user_db query
returns a uid column and a gid column containing the numeric uid and gid
of the owner of the directory, then dovecot should have no problem using
mail in these folders. Is that correct?

(I'm actually getting permission errors appear in the log file on the
directories when I try and attach with a client, which reports "Cannot
get LIST information for pattern `*' on IMAP server a.b.com unknown".)

thanks 
Glenn