Someone up-thread noted that my personal domain is hosted on google groups. I've noticed in the past that the behaviour of gmail.com can be very different from the behaviour of a paid mail domain like mine...
Google says that every user's spam filtering is different. It's not just free vs. paid.
Agreed that spam filtering today is a hard problem, and given Google's scale their problem with it is bigger than most others'. My assertion is that given how ubiquitous mailman's administrative messages are (as opposed to random list traffic), and given that those messages haven't changed in structure in aeons, it should be trivial for a company with Google's resources to not get false positives on those messages.
Imagine if some spammer tried sending spam formatted like fake mailman admin messages hoping that the spam filters will let them through since they're obviously OK. Yes, spammers do that kind of stuff. Or maybe users are tired of the useless monthly messages and report them as spam. Regards, John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly