Is there any reason the "You have been added to" email itself couldn't be set up for bounce detection/processing?
That would give me an earlier validity test for typos on the handwritten and transcribed email addresses from my PTA members.
Likewise an Invite (if they aren't already), and any notification to a member or moderator.
My thinking is that we've seen (in Yahoo Groups) circumstances where an email service rejects a small fraction of the presented messages, and that fraction may be sensitive to the type of message (message content). In those cases, when you know you didn't get a notification (of say, a pending message) it would be very helpful to have the evidence to present to the mail service.