Login into your mailing list admin page. Select “Privacy Options” and then “Sender Filters”

To automatically accept non-member posts from a given domain, enter the following text in the “accept these nonmembers” setting:

^.*ucla\.edu

where “domain” is replaced with the domain you want to accept. For example, if you want to automatically accept all messages from UCLA email addresses, you would enter “ucla.edu” as your domain.

You can do similar things with the “hold these nonmembers,” “reject these nonmembers” and “discard these nonmembers” settings. For example, if your list receives lots of spam from the xyz.com domain, enter “^.*xyz\.com” in the “discard these nonmembers” setting. Messages from any address ending in xyz.com will then be automatically discarded.