[Mailman-Developers] Running scripts when subscriptions recieved

[foobar at eh.net]

I run the mailing lists for a mid-sized academic site (http://eh.net). We
recently switched over from a legacy Listproc installation which was
highly customized and was falling apart.

We deal with a lot of spam at the site, however, and we're looking into
setting up TMDA (Tagged Message Delivery Agent), a blacklist/whitelist
system. One of the things we'd like to whitelist on a site-wide basis (not
just for the list email, but for the administrators' addresses as well) is
a list of current and past subscribers. Now, the issue arises of how to
keep such a system *current*.

What's the best place in the Python code to hook into so that I can get a
script to run whenever a subscriber joins a list? Optimally, this should
also be able to call the script with the address of the subscriber as an
argument, so that a sitewide resync is not necessary per address.