I don't see a login date for the mail_user table. How do you determine which mail accounts are being used? It would be nice if there was a LAST_LOGIN_DATE field in the mail_user_table so that we could just sort on that field and see what accounts have been abandoned.
If you add such a field to the database and update the value every time a user logs in, you will have a dramatic increase of db-connections / updates. You can run grep over your logs to get a list of users who used the mail-server.
Hmm maybe is might not be a bad idea to add a toggle to allow the updates. That way you can just take the performance hit for 24 hours so that you can tell. Otherwise, including a script that does the grep for you might help. I don't know of any admin that wouldn't have to do this at regular intervals.
