Receiving a "You have been unsubscribed" email when not actually unsubscribing

[RS]

----- Original Message ----- 
From: Peter Corlett 
Cc: get_iplayer at lists.infradead.org 
Sent: Tuesday, April 19, 2016 10:15 AM
Subject: Re: Receiving a "You have been unsubscribed" email when not actually unsubscribing

...
The likely reason Google is bouncing some list mail is that a few spams have
been forwarded to list subscribers, and that's given the list itself a lower
score.

I got one last week which used the UTF-8 character set and Base64 encoding to send spam in Chinese characters.  From the headers it looked as though it had been forwarded by the list server.  It seems the list server will reject messages which misuse In-Reply-To (and as I don't use a threaded email client I didn't even realise that was a problem) but does not check the message is in Latin characters.