use LMTP process to do checks & dispose messages earlier
Original LP Author: Sumana Harihareswara , LP Link: https://bugs.launchpad.net/bugs/1414163
Hook into the LMTP process http://wiki.mailman.psf.io/DEV/LMTP%20process so that messages can be disposed of as early as possible. Check potential senders and recipients at LTMP time to check, e.g., "are you sending to a list that does not exist or that you do not have permission to post to?"
From http://wiki.mailman.psf.io/DEV/Mailman%203.0?action=diff&rev2=30&rev1=28 -- a TODO for the Mailman 3.x series.