mailman - partition virtual domain name?

[Noah]

mailman-2.1.4
sendmail-8.12.11
freeBSD-4.9-STABLE

I am placing listnames in the /etc/mail/aliases file to have the forwarded to
mailman for processing.  

I running virtual hosts on a machine and I want to stop people from sending to
listname at domain1.com and only allow people to post to listname at domain2.com

currently users can post to both listname at domain1.com and listname at domain2.com

thank you,

Noah