I'm impressed by Philip Bondi's use of mailman[23] for home financial automation. ("Take off Eh!") ... It seems like a ticketing system would be a better system for such a use... maybe the IETF SML WG will further help with this.. (I find most Canadian financial institutions are so far behind the curve)
I think that your email is hosted by hostedemail.com? I'm guessing that "eshop" is the mailbox you use for these common notices, and maybe you retrieve that into your mailman3 with fetchmail or something? Or does your ISP turn around and SMTP to you directly? Is it your MTA, their MTA, or mailman that is doing the rejection?
My problem, on lists.sandelman.ca aka lists.tcpdump.org, is messages that appear to have been processed by my MTA (according to postfix logs), but which are never delivered, nor held. Lost somewhere in mailman3 queue. Sometimes they show up after a host reboot.