[Mailman-Users] list member address parsing question

[admin2]

Hi list,

Somebody suggested me ask the mailman folks this question.

My google official account username is <blah at domain.com> but I have 
verified and activated another email address "sample at domain2.com" .  I 
am able to originate email with "sample at domain2.com" in the "from" email 
but mailman still rejects the message claiming "Sorry, only subscribers 
may post."  Mailman thinks I am not a member of the list and is 
considering me "blah at domain.com" even though I can see in the bounce 
that "sample at domain2.com" is in the From portion of the header.  The 
SMTP header of the bounce claims "Received-SPF: pass", "Return-Path: 
<blah at domain.com>", and "Sender: <blah at domain.com>"

When I send the same mail through a domain I administer the email 
"sample at domain2.com" is properly identified.

Is there anything more I can configure to appease mailman's legitimacy 
checking?

Cheers,

noah