Hello,
E.g.
you may create a filter for the X-Spam-Score header added by SpamAssasin,
and set a value such as [^+]*[+]{4,} so all emails with a x-spam-score
value equal or more than 4 get rejected/discarded (at the admins' wish).
I
don't quite remember right now, but I think mailman3 header filters do
apply to subscribers as well, even if their moderation policy is set to
"accept immediately", as apparently these rules seem to apply on top of
every other rule/setting and one must be careful, but a SpamAssasin
value of 4 or more should be pretty safe/accurate though.
What I miss in mailman3 (and existed in mailman2 IIRC) is the possibility to hold for moderation messages from new subscribers only (getting automatically removed from the moderation queue after X days and/or Y accepted posts), instead of the current all-or-none approach (I've been looking for that option but it seems not to exist anymore).
Best regards, M.