I use dovecot on a machine where users without an existing home directory (Not my idea...) need to access their mailboxes. Unfortunately dovecot tries to chdir to the users home directory before allowing IMAP access - is there anything I can do about that besides creating a dummy-homedirectory for these users?
I have a similar set up; none of the mail accounts correspond to an account in my passwd file. I have a postoffice account in the passwd file that owns the /var/mail directories where mail is stored. I use LDAP to assign each user the UID number for the postoffice account so that Dovecot's imap process can work with their mail. The postoffice home directory receives the raw log entries, and the account runs some related cron jobs that help manage the mail. So basically, I have one Unix account and home directory to handle all mail users. If you don't want to deal with LDAP, you should be able to do something similar with PgSQL, or perhaps one of the other supported user databases. The key is always passing the postoffice UID number to Dovecot, regardless of the user.
You can accomplish this with the static userdb:
auth_userdb = static uid=210 gid=210 home=/var/mail/%d/%n
...or something to that effect.
-- Alex Howansky Wankwood Associates http://www.wankwood.com/