I've searched the forums and wiki for an answer to my question and couldn't find any. I'll appreciate any feedback.

I would like to restrict the sender domain name.
i.e, if my domain is, I would like only
messages coming from "MTA Trusted Networks" or Authenticated users to be able to be from, and no one else.

Today the situation is that spammers send messages to my users at as forged address coming from

Thanks in advance,