Readdress domain root origination address

[thndrbrd]

How difficult would it be to ensure that monitoring / reporting emails from Unix systems would
_Always come from?_ Super-User [root@domain.net] _As opposed to these?_

Super-User [root@machine1.domain.com]
Super-User [root@machine2.domain.com]
Super-User [root@machine3]
Super-User [root@machiine4]
Super-User [root@machine5.domain.com]

I am trying to filter spam and it would be easy if i only had one address root@domain.net to capture.
Does this make sense? My environment has one mail relay box for this private domain and it all sets behind a firewall. Should address alises or reqrites be done on the clients .cf file or on the mail relay .cf file. If so how?

Thanks in advance ....