[CentOS] OT?

I have a CentOS server with postfix running. A pop user's account was compromised and a lot of spam started being sent. My upstream ISP's mail program started refusing to talk to me because of the very high rate of mail, error 451. I disabled the compromised account. I then changed the postfix settings to deliver mail directly and flushed the mail queue. This resulted in spam being sent out.

There were about 20K mails in the queue. I don't know how I might have handled this better, I would have preferred to not send the spam, but the volume was large and the labour of sorting out spam from legit email was prohibitive.

Advice? A better list for this issue perhaps?

Dave