Bingo. Maybe not the solution, but it's gotta be connected somehow, I believe.
On 20180217, both Gene Heskett and myself unsubscribed then resubscribed to
the mailing list.
If I recall aright, Gene was having problems, and I was having some kind of
problem sending or receiving to the list myself, so I decided that I would
resubscribe, as well.
The time doesn't match any of those emails, but both these events occurred on
the same day.
This doesn't explain the emails to and from person B, who isn't a member of
the list. I checked my correspondence with her, and there were no emails on
that date.
Does this make sense to anybody out there? I can see the correlation, but no
actual causal relationship among any of the parties involved.
Bill