This comment is from https://mail.python.org/pipermail/mailman-users/2018-June/083453.html
If you want an umbrella list to post anonymous announcements to several sublists at once, always getting the appropriate footer from each list, and not allowing sublist members to post, follow this procedure:
1. Create the umbrella list and set it up as anonymous (General Options > anonymous_list) and as umbrella (General Options > umbrella_list).
2. Add the sublists' posting addresses as members of the umbrella list.
3. Either add the addresses of people allowed to post to the umbrella as umbrella members, or authorize them to post as nonmembers (Privacy > Sender filters > accept_these_nonmembers).
4. In every sublist, put the umbrella's posting address as accepted non-member (Privacy > Sender filters > accept_these_nonmembers).
5. In every sublist, put the umbrella's posting address as acceptable alias (Privacy > Recipient filters > acceptable_aliases). This last step is necessary only if require_explicit_destination is set to 'Yes'.
If you don't get the expected results, check the /var/log/mailman/vette log and the value of the USE_ENVELOPE_SENDER directive in mm_cfg.py or Defaults.py.