Mark Sapiro writes:
Presumably that's the 'Recipient address rejected: User unknown in virtual alias table' message, but I see no virtual_alias_domains in your posted main.cf.
I'm pretty sure that what's going on here is that the message is coming in from outside, Postfix runs down the various relays (including local delivery) available, none matches, the last in line is virtual aliases, and that table is empty so the user is unknown.
That's the only way I can see the sender_canonical_maps variable affecting *recipient*-based decisions, by making it look like the sender is local, and so enabling delivery to non-local addresses. Why a Mailman list appears to be non-local is a question I am not sure. My guess is
myhostname = localhost
because Postfix doc says mydomain "is derived from $myhostname by stripping off the first part (unless the result would be a top-level domain)," so literally "localhost" is the only deliverable domain left, and some-list@the.actual.dom doesn't work. Except that the.actual.dom should be in postfix_domains.db, so ... ????
Steve