I'm not sure of the best place to post this but thought it was worth mentioning. Years ago with VB we used to have a newsletter addon which sent out "newsletters" via PM to all our members. Today someone replied to one of those very old PMs... Cue a giant conversation including hundreds of users who then replied in confusion causing it to snowball and send loads of email notifications. It might be useful to have some kind of PM management (sender lists, not content) in the ACP but I'm not sure how that'd work.