Currently, whenever Mailman delivers a message to a list, a
Sender' header is appended. As RFC822 specifies that there should only be at mostSender' header in any message, appending
is not right if there already is such a header present (e.g. whenever
the senders MUA added a `Sender' header).
The included (untested, but simplistic) patch (against current CVS Mailman) tries to fix this.
[ However, I suspect my patch might not work for messages already containing multiple `Sender' headers when Mailman receives them, as Message.SetHeader doesn't appear to really be "crushing duplicates" in those cases. ]
To cater for umbrella lists, similar fixes should probably be applied
Errors-To' andX-Mailman-Version' header appending in