On 13/06/16 17:36, Nicolas George wrote:
Solution 1: ask every people who reply to A, i.e. people who do not care about the unwanted CCs, to make a (moderate) effort without getting any benefit for themselves. Solution 2: A makes the moderate punctual effort to configure the MUA to set the header correctly and directly reaps the benefits.
Solution 3: A makes the probably-smaller-per-incident effort to set up filters dropping on the floor any mail sent by the people whose MUAs have bad default behaviour on Debian mailing lists.
E-mail sent to the Debian mailing list contains sufficient information in its headers that reasonably-written MUAs should not have difficulty detecting that it is mailing list e-mail and behaving appropriately by default.
The List-Id: header is set, indicating (a) that it is a mailing list message and (b) what list it was sent to, and the List-Post: header is set, indicating how to send messages to the list.