Block/Filter Sending mails to a specific domain
I'm looking for a way to block all mail send to a specific domain @example.com from @mydomain.com.
I had been searching for this in the forums, wiki and google and no luck at all, I found a lot of info on blacklisting incoming mail but not outgoing and limiting certain users to send mail to specific domains.
But what I'm trying to do is different cause I want to block/filter all my users trying to send mail to that specific @example.com domain, if you can even send just a reply mail and not blocking will work too.
Sorry if this was covered already but I couldn't find it.
Thanks for any help you can give me.