After about three months of trying to get secureserver.net to fix their highly-broken systems, I'd like to block all emails destined to all virtual domains hosted by them. However, I'm not quite sure how to do this with my setup.
I'm using postfix as a smarthost to forward mail through my upstream ISP. Is there any way to have postfix resolve the MX record of the destination domain and block outgoing mail on that basis? -- "Oh, look: rocks!" -- Doctor Who, "Destiny of the Daleks"