Recently, one of our users suffered identity theft and their email account was taken over by spammers. We didn't find out about the problem until after our domain got blacklisted. I want to keep this from happening again.
Is there any way to rate limit outbound messages on a per user basis? For instance any user can only send 100 messages per day. We run Exchange 2007, but I'd be willing to set up a separate server if I need to use Linux or some 3rd party SMTP server.