Restrict incoming domains
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 example.com, I would like only
messages coming from "MTA Trusted Networks" or Authenticated users to be able to be from example.com, and no one else.
Today the situation is that spammers send messages to my users at example.com as forged address coming from example.com.
Thanks in advance,