Re: [Dovecot] Well, "Hard filesystem quota can also be problematic"

Jeroen Scheerder wrote:

that may not be there; perhaps file system quota's, along with a solid delivery agent (such as procmail) and a strategy of making sure there's sufficient storage for mailbox writes by the imap server, as sketched before, will suffice?

Don't know if it helps you (didn't even read the whole thread), but there are MTAs (at least Exim) with builtin delivery and quota handling.