The mailing lists are now running with the standard Debian packaged version of Mailman.
The Mailman setup for Exim is in /etc/exim4/symbiosis.d/20-routes/11-mailman and /etc/exim4/symbiosis.d/30-transports/11-mailman. It's standard Mailman/exim setup.
There is one non-standard extension, the LongSig handler. I have copied the Python code for the LongSig handler into /usr/lib/mailman/Mailman/Handlers.
LongSig is currently enabled only on accu-general. The process is described in this Mailman FAQ item. The input filename for the modified accu-general pipeline is in /etc/mailman.
Given the appropriate Mailman login, you can create a new list from the web interface.
Unfortunately, it appears that while the list is created, some of the list files lack the correct permissions.
# chown -R list:www-data /var/lib/mailman/archives/private/<list-name>*
appears to be necessary.
There are lists which have been moribund for a while, and which we have disabled, to save the list admins from having to handle spam messages.
There is no official way in Mailman to disable a list. The closest you can get to is emergency moderation, which just makes all lists moderate every post.
So I've disabled the mailing lists by chmod 000 /var/lib/mailman/lists/<list>. Also, I've modified the Exim Mailman router to check explicitly that the list file is accessible by group list:
mailman_router:
debug_print = "R: mailman_router for $local_part@$domain"
driver = accept
require_files = root,list:MM_HOME/lists/$local_part/config.pck
local_part_suffix_optional
local_part_suffix = -bounces : -bounces+* : \
-confirm+* : -join : -leave : \
-owner : -request : -admin
transport = mailman_transport
This means that the list address is no longer routable, and the list no longer appears on the list of mailing lists. All list configuration and archives are preserved.