On Sat, 05 Dec 2009 00:07:36 +0600
Mikhail Gusarov <dottedmag@dottedmag.net> wrote:

> The only problem with Cc is that Mailman suppresses duplicate
> messages and hence there is no List-Id: on message.

Err, this makes no sense.  How can Mailman have any knowledge of, and
therefore "do anything" to any message that came by way of a CC?

Now, your mail transfer agent might do duplicate suppression, and if
the direct email reaches you before the one that went through the
mailing list, you won't have a copy that includes the list-id header,
but that's an issue on your end, not with the mailing list software.

Mike.