we have 2 "mail" servers, one our "mail relay", this is a server which relays the domains we have in our organizations, (Thats why i use Mail relay and on our IT department everybody then knows about which server we talk about ) and scans the incoming and outgoing massages, the messages that are allowed and are clean then send to our internal Exchange.
We can send not to al our users needs because they use spamcop.net as blacklist