Hi everyone,
In Mailman2 some lists would ban everyone and then manually add subscribers who should be on the list. In Mailman3 this is no longer possible, the ban list trumps everything. If an address is banned, messages from it will be silently discarded, regardless of whether they're subscribed or any other options.
We have so far either removed these kinds of bans during imports or held off importing these lists yet.
Please review your list's ban list ("Ban List" tab in Postorius) and remove any overly broad ones.
As a sidenote, we now have the ability to enact global bans, so if there's a domain or pattern spamming across multiple lists, we can block it in one spot.
I've also added this information to https://meta.wikimedia.org/wiki/Mailing_lists/Mailman3_migration#Review_bans.
-- Kunal