Oh, interesting... so you mean if I set up the shell account first and then use that as an email account, the email WILL be stored under the shell account? It never occurred to me to try it that way.
I also thought of another much more generic method... a script that acts like an imap client which you call from a crontab. It would be able to log into any regular imap server and executes imap commands to move the messages from one folder to another as if it were just another imap client. This solution should then work for any imap server anywhere.
Does anyone know if something like that exists out there?