[Mailman-Users] Where in the code is the message footer added?

[C Nulk]

Hello all,

Some of the users at my site send/post their messages in HTML format. 
As we know Mailman does its best to add the list's message footer.  At
our site (with HTML formatted messages), the footer usually appears as
an attachment (generally called Part.002 or Part.003, etc.).  The
message footer contains the url on how to unsubscribe.  However, our
users cannot seem to find the footer in one of the attachments.  They
think the 'Part.002' is just gibberish and don't look at it. 
Training/educating the users is not an option since we already do that
and our users seem to be determined not to remember or understand.

What I would like to do is give the message footer attachment a name. 
That way instead of seeing 'Part.002', the users will see
'Unsubscribe'.  Maybe that will help, maybe not but it is one more step
to make it a little more visible for the users.  I am guessing I can use
'Content-filename: <name>' to give the attachment and name.  The
question is where in the code do I add the change?

Thanks,
Chris