I'm sending this to the ietf list because mailman is widely used for IETF mailing lists. Recent versions of mailman appear to have a flaw that allows the sender of a message to send a copy to everyone in a mailing list _except_ some set of explicitly specified recipients, and there will be no indication that those recipients were excluded. In the context of an IETF mailing list this can be used to exclude participation by certain individuals. Specifics: Mailman has a per-recipient setting called "nodupes". The effect of this setting is that any recipient address that has the nodupes flag set, and which appears in a To or CC field of a message sent to the list, will not receive a copy of the message from the list. It also appears (from emperical testing with a limited sample) that the list may also remove that recipient's address from the CC field of the copy of the message sent to the list. Recent versions of mailman set "nodupes" by default. List participants can change it if they know about it, but they might have no idea of how this setting works and how it can be used to exclude them from participation. The workaround is to set "new_member_options" (under General Options) so that "Filter out duplicate messages to list members" is NOT set. "Do not send a copy of a member's own post" should probably not be set either. Keith _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf