[META] Why are duplicate posts coming through?

[nospam.Chris Angelico]

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