[Mailman-Users] Mail to list returned

[Homeport]

My mailman installation seems to be working fine but when I send mail to 
the list I get this response:

usna-alumni at usnaweb.org; Action: Failed; Status: 5.1.1 (bad destination mailbox address)
    Remote MTA usnaweb.org: SMTP diagnostic: 550 5.1.1 
<usna-alumni at usnaweb.org>... User unknown

Do I have to establish an explicit user for each mailing list?
If so, how do I pipe mail to Mailman?

If not, what am I doing wrong?

Thanks, 

--Ray

Ray Trygstad
Editor, http://homeport.usnaweb.org/