A couple of thoughts:
There are 3 sections of questions related to reducing spam, at the bottom of https://meta.wikimedia.org/wiki/Talk:Mailing_lists/Administration if anyone has tips/answers?

I've added details on a useful greasemonkey script (written by bd808), that greatly speeds up the moderation process of discarding spam and adding addresses to the auto-discard list, in a subsection of https://meta.wikimedia.org/wiki/Mailing_lists/Administration#Tend_to_pending_moderator_requests

HTH,


On Thu, May 4, 2017 at 7:30 AM, Lodewijk <lodewijk@effeietsanders.org> wrote:
Totally feel with you. I had to fully auto-reject non-members on other lists for the same reason. 

It would be helpful if more spam would be rejected right away (e.g. if a message is rejected/explicitely ignored in more than two mailing lists, you can ignore them elsewhere, too). 

Lodewijk

On Thu, May 4, 2017 at 4:16 PM, Maarten Dammers <maarten@mdammers.nl> wrote:
Hi everyone,

For quite some time I have been one of the people maintaining and moderating the different Pywikibot mailman lists. Over time the amount of junk (spam) coming in through the -owner addresses of these lists has increased a lot. My impression is that the people in charge of maintaining mailman are not doing enough to fight this kind of abuse. I'm so annoyed by this I decided now is a good time to stop maintaining mailman lists and spend my time on something more fulfilling.

Maarten


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Nick Wilson (Quiddity)
Community Liaison, WMF