This is probably related to https://phabricator.wikimedia.org/T232417 

On Fri, Apr 23, 2021 at 11:10 AM Pharos <pharosofalexandria@gmail.com> wrote:
All of the yahoo addresses seem to be simultaneously unsubscribing from our mailing list.

Is this related to the upgrade?

Thanks,
Richard
(User:Pharos)

On Wed, Apr 21, 2021 at 8:46 PM Kunal Mehta <legoktm@debian.org> wrote:
Dear Wikimedia mailing list admins,

As you may have heard, we will be upgrading the mailing list software to
Mailman 3, which is a full rewrite, fixing lots of long standing issues,
especially around security. A short list of improvements:

* One user account (no more monthly password reminder emails or list
passwords)
* Ability to search through archives
* Posting through a web interface
* A web interface that doesn't look like its from the early 2000s

For the most part, if you just send and receive mail from the list,
nothing dramatic will change.

A test installation is available at <https://lists-next.wikimedia.org/>
if you'd like to take a look now (all data will eventually be deleted).
We can import your list into the test system so you can look around the
new interfaces, make sure settings were migrated correctly and archives
display correctly.

We're still finalizing the exact dates, but we may start migrating
mailing lists starting next week. They'll be migrated in batches,
starting with lists with no archives, and then going by size of archive
and # of subscribers. Expect very big/old lists (wikimedia-l,
wikitech-l, etc.) to go last. We plan to send a notification to the list
admins when we start migrating the list and once it's finished.

We will need help from list admins to make this go smoothly.

* If your list is obsolete or should be archived, please add
"[OBSOLETE]" or "[ARCHIVED]" to the list description and we'll take care
of the rest.
* Please update your list description to indicate who the list admins
are (either usernames, email addresses, etc.)
* If you'd like to volunteer your list to go early, let us know.
* On the other hand, if you think your list needs special handling and
should go later, let us know as well.
* It is our intention to have all mailing lists be publicly listed,
please let us know if you have a reason that the existence of your list
should be kept private.
* If you've lost track of all the lists you're responsible for, we can
look it up for you :)
* The canonical URL of your mailing list will change. If you link to
your mailing list in help pages, templates, etc. You should update it
after migration. For example
<https://lists.wikimedia.org/mailman/listinfo/wikitech-l> will change to
<https://lists.wikimedia.org/postorius/lists/wikitech-l.lists.wikimedia.org/>
(we expect to provide redirects).
* For public archives, we will ensure that archive links will not break.
For private lists, we do not intend to support old archive URLs - if
this is a big issue for you, please let us know.

There's probably stuff we missed to mention, if you have questions,
concerns, comments, please let us know on this list or #wikimedia-tech
on IRC.

For tracking the work see https://phabricator.wikimedia.org/T280322

Thanks,
Amir (Ladsgroup) and Kunal (Legoktm)

_______________________________________________
Listadmins mailing list
Listadmins@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/listadmins

By sending a message to this list, you email all admins of all lists. To request technical changes for a specific list, instead create a task in Phabricator. See https://meta.wikimedia.org/wiki/Mailing_lists
_______________________________________________
Listadmins mailing list
Listadmins@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/listadmins

By sending a message to this list, you email all admins of all lists. To request technical changes for a specific list, instead create a task in Phabricator. See https://meta.wikimedia.org/wiki/Mailing_lists