J,

Can someone please tell me the title of the bounce probe message, so I
can alert people what to look for?

Subject: Your Groups.io Account Is Bouncing
https://groups.io/g/GroupManagersForum/wiki/10614

That example was collected over a year and a half ago, so there may have been changes since. I didn't collect a fresh example because, for whatever reason, I didn't receive a bounce probe - I learned my account was in Bouncing status when I went to the web site.

Depending on how promptly the first Bounce Probe is sent, it may also bounce, which is what I believe happened to mine (it did not go into Spam, Trash, or other Gmail folders).

I would not be surprised if so many bounce probes are going out that
they're now being judged as spam and going into spam folders.

Seems possible. Fortunately (?) this incident affected Gmail users, and Gmail tends to be better about discerning spam versus ham than most.

Shal