Arch Linux mailing list changes

As part of dropping Python 2 which is EOL, we have migrated our mailing lists from mailman2 to mailman3.

Rewriting of the "From" header and subject (to prepend the list name) have been disabled to keep the DKIM signature intact. This means "reply to mailing list" must be used when replying to the list and you may need to update your filters and rules matching the "From" header.

All existing subscriptions are migrated and you do not need to re-subscribe. For managing your subscriptions a new mailman3 account must be registered.