Mark; while investigating something else entirely I think I have found a bug in the detection of some members being "bouncing" but not recorded as such.
This perceived problem seems to arise if a member has their delivery set to Special Notices Only; in the group I co - own they should still receive monthly notices because these are sent as Special Notices, but I have found several instances where these have been bounced for several months or even longer. However, there is no "Bouncing" Status badge against these members in the Members List.
I have concluded - perhaps wrongly - that where a member has selected Special Notices Only a message bounce will not be automatically further investigated by system - generated Bounce Probes. A little further delving revealed the point that as the individuals are not listed as bouncing a Moderator cannot send a Bounce Probe manually, which most of the time makes sense.
Can you confirm (or otherwise!) my conclusion that a "Special Notices" member will not have system Bounce Probes sent to them in the event of a bounce occurring is correct? If my belief is correct then I think this configuration is wrong; any bounced message should be followed up by bounce probes and the member badged accordingly.
In some respects this doesn't matter but I could easy see it mattering for any group hovering around the threshold where payment for member numbers applies; members recorded as Bouncing don't count towards the trigger point but if they aren't logged as bouncing then they will be included as "valid" members even when they aren't because of their unrecorded bouncing status.