auto deleting mail from removed users on

When a user has left the company and the mailbox has been deleted (rightly or wrongly)or mail is sent to a user’s name that dosen’t exsist,(as in spam) how can I auto delete it without it going into the admin account for checking.
I.E. users who subcribe to e-mail notifacation and are no longer employed, and there isn’t and easy way or getting them removed from the senders list (auto remove not working on senders side), but other people in the company still want to recive mail from the same sender, (so it’s not spam), such as techrepublic notifications.
I want to have only that users mail dumped if it’s from a certain domain. How do I set this up? Do I have to make the mailbox again and spam it, which creates an admin issue!