That was my understanding too.
Positive (no entries for the original PM in sent or skipped logs, mail was not delivered via mailgun).
And just to be absolutely sure, I tried again just now with the same user
- as member of a custom group
- and as a moderator
and as expected, the custom group email was logged as sent right away, and when I was sure the issue was confirmed, the email for the moderators group was also logged (and delivered via mailgun), but with a few minutes delay.
I have no Idea if this is an intermittent error or not, but I’m sure it’s not working reliably right now, and I would be willing to investigate further if you can provide additional guidance on where to look.