Mailman 2.x --> ... Mailmand 3.x ?, or ...

So,

Interesting data point I stumbled across.
Migrating off of Mailman 2.x (no longer supported, because Python 2), to
... potentially Mailman 3.x, and sure, lots of pros/cons about doing
that, vs. other potential list software.

Anyway, one data point I'll throw out there:
IETF.
Yeah for at least many of their lists (more than 400, but not more than
600), they're using Mailman 3.x.  And the way they've got it set up and
configured, looks pretty well polished.  If one is curious, have a look:
https://mailman3.ietf.org/mailman3/lists/?count=200&all-lists=
And not exactly a low visibility low risk application.
Certainly high visibility and also gets quite the volume of usage,
so not at all trivial.  And I'd certainly also presume,
given what IETF is, and their resources (direct and indirect),
was probably a quite careful decision and with a lot of testing and
vetting.

Anyway, doesn't at all mean that Mailman 3.x would be the best choice
for all, or even necessarily most, but thought it to be at least one
interesting and rather noteworthy data point I'd throw out there (and
beside's that of GNU's lists, since Mailman is itself GNU authored
software - so at least they eat their own dog food).

The other list software that I find quite impressive and would probably
also consider a very viable path, other than Mailman 3.x (though of
course not as compatible(ish) with Mailman 2.x, so would be bit rougher
of transition), would be what Debian uses for its lists ... SmartList
(package: smartlist), which works atop procmail.  Much simpler and
cleaner than Mailman 3.x (which has whole lot 'o bells 'n whistles,
nice - sure, but adds a whole lot of complication, etc.).  Haven't
looked into it in detail, but it seems it's highly well able to do the
needed, without too much work/hassle.  Wish I could say likewise of
Mailman 3.x ... not horrible, but it is a rather large complex beast.
And Smartlist, along with other relevant configured bits, also nicely
handles archiving for web, including nice persistent URLs,
which if I recall correctly key off of Message-ID: header data,
so, e.g. reimport/reindex and, if messages were added/dropped, all those
common to both, still same persistent URLs (unlike Mailman 2.x where
they'd shift).  I'm also guessing Debian has a moderate bit of addidonal
stuff they've layered on, e.g. for some of their list statistics images.

Alas, I still run across a lot of sites that are still on Mailman 2.x

Anyway, just some observations.

See also: https://lists.debian.org/