[Mailman-Users] How to PRESERVE multipart/mixed format

[andReadG]

Hi guys

My question is this:
I have allowed attachments in Mailman, but whenever
someone sends a mail to the list, its subscribers
receive the original message coverted to text/plain
with a link to the attachment(s).
The link is correct and everything works in the
end, but I would prefer the original attachment to
remain within the original mime multipart message!
Can it be done?
(note: the actual MTA is postfix)

I hope I'm not asking something naive!

Thanks for any suggestion