[META] Why are duplicate posts coming through?

Sun Nov 26 17:53:51 EST 2017

Not sure whether this is an issue for -owner or not; apologies if not.
I'm seeing a whole lot of reasonably-recent posts getting re-sent,
with "nospam" attached to the posters' names. And they're getting
re-sent multiple times. Sometimes the posts have encoding problems
(small amounts of mojibake).
What's going on? Is there something going haywire with the news/mail
gateway? Is there a rogue client re-posting a bunch of news? Somebody
testing something?
ChrisA