[$] A SpamAssassin surprise

Here is a piece of advice for anybody wanting an easy and frustration-free
life: do not run your own email system.  While there numerous advantages to
keeping some control over your communications, there is also a long list of
things that can go wrong.  A recent failure of spam filtering on the LWN
email system illustrated one of those ways, as well as shining a light on
how even a seemingly independent email system is tied to other services
across the net.

https://lwn.net/Articles/987566/