Mail Group Restriction?

[TWGMedia]

Hi all! I had a client that used a a mailgroup for sometime but switched to mailman because they felt they were getting a lot more spam through a mail group as opposed to mailman where if the sender wasn't on the list, the message did not go through.

The issue is apparently they want the functionality of the mailgroup with a degree of restriction.

Is it possible to setup a mailgroup so only email addresses from a specific domain name can send to the mail group(s).

Thank you.

Kevin