Comment 1 for bug 1721746

This is not a security issue in Mailman. Yes it is possible to spoof a list member's address in various headers to cause a post to be accepted by a list, but there's nothing Mailman or any list management software can do about that short of moderating all members.

Also, see <https://mail.python.org/pipermail/mailman-users/2017-October/082558.html>, <https://wiki.list.org/x/4030556> and the "How to post to the announcement list:" section at <https://wiki.list.org/x/4030685>.