[Cialug] Postfix stumper

[L. V. Lammert]

Building Mailman 3.1 in containers, .. postfix on the host is working
outbound, but inbound is a stumper:

Recipient address rejected: User unknown in relay recipient table;

main.cf:
--------

transport_maps =
    regexp:/u/Data/mailman/core/var/data/postfix_lmtp
local_recipient_maps =
    regexp:/u/Data/mailman/core/var/data/postfix_lmtp
relay_domains =
    regexp:/u/Data/mailman/core/var/data/postfix_domains

local_recipient_maps:
---------------------

# AUTOMATICALLY GENERATED BY MAILMAN ON 2021-08-03 19:19:35
#
# This file is generated by Mailman, and is kept in sync with the binary hash
# file.  YOU SHOULD NOT MANUALLY EDIT THIS FILE unless you know what you're
# doing, and can keep the two files properly in sync.  If you screw it up,
# you're on your own.

# Aliases which are visible only in the @mailman.dd.org domain.
/^test_list at mailman\.dd\.org$/                  lmtp:[172.18.0.10]:8024
/^test_list-bounces(\+.*)?@mailman\.dd\.org$/   lmtp:[172.18.0.10]:8024

Mailman appears to be configured properly:
------------------------------------------

bash-5.0# cat /etc/postfix-mailman.cfg
[postfix]
transport_file_type: regex
# While in regex mode, postmap_command is never used, a placeholder
# is added here so that it doesn't break anything.
postmap_command: true

Whereas:
--------

myhostname = mailman
mydomain = dd.org
mynetworks = 127.0.0.0/8, 172.18.0.0/24

Can't figure out how to determine the exact failure - it would seem that
postfix thinks it's local domain is a relay. Any thoughts would be
appreciated.

	Thanks!