[Mailman-Users] To Domain Is Wrong

[PNIXON at ci.somerville.ma.us]

Hello,
 I've setup a list server inside my dmz, and I want all the emails to
appears to be coming from lists.somerville.ma.us, but they keep showing up
in the To and From Headers as from rosie.somerville.ma.us

rosie.somerville.ma.us is the actual hostname for the box.

Any suggestions or things I should check?

Thanks for all your help!

--Pat