[Mailman-Users] Default ban_list for new lists

[Edward Ned Harvey]

I have a mailman server, where port 80 is only accessible within the
company, but port 25 is open to the outside world.  It is intended for
internal mailing lists only.

I want to close the hole, where a malicious user can subscribe via email,
who isn't part of our domain.  I easily created a ban_list for
^(?!(^.*@mydomain.com))  and this is applied to all existing lists.  I would
like this ban_list applied by default to all new lists.

I've seen many such default defaults, under mm_cfg.py, but haven't found one
for the ban_list.  Is there some way I can set this?

Thank you.