Block spam emails from local Domain name

[nuskope]

We have recently been getting reports of spam emails from our own domain name addresses.

My question is is there a setting in the spam filters we can apply that will block all emails from @domain.com that didn't originate locally? (users should only be able to send @domain emails from this one server)

ie.

[email protected] can email [email protected] providing he is useing our outgoing server (local delivery)
[email protected] isnt useing our outgoing server and when the email arrived into the filters its marked as spam.

 

[Infopro]

In your cPanel > Mail section > Default Address, what do you hate this set to here?

All domains on this menu should be set to:
Discard with error to sender (at SMTP time)
With some sort of message like:
No Such User Here