the common MUA that recognizes this header, and are not computer savvy-enough to know how to turn this "feature" off. That would tend
The person who complained about it to me, was able to turn it off, but he didn't want to do so, claiming that he needs it sometimes to inform people writing to him in private that he read their e-mails. He is using The Bat, and he set it that way, that it was poping up a window telling him that someone sent an e-mail with x-confirm-reading, and he should either accept it (send a confirming message) or deny it. He claimed that list-owners should configure their mailing list programs to remove that kind of headers, that it should be within their basic tasks to do when configuring a list. Well, I couldn't argue much with that. There should be indeed such a feature in Mailman like it is in ecartis: a form where could be set colon separated headers to be removed from outgoing messages: http://znik.wbc.lublin.pl/~ak/rozne/ecartis/freelists_config.gif
Regerding MTA. I'm not the admin of the server, and I have no acccess to it. Besides, I don't think it would be a good thing to do it on MTA level (other people could complain...), it should be possible to do within Mailman by list-owners.
ak