With {T278610} being done soon. We will start migrating mailing lists to the new mailman in batches.
These are the batches:
[x] Group A: Mailing lists that have archiving disabled. (44 mailing lists: P15505)
[x] Group B: Mailing lists with mbox archive below 100KB (98 mailing lists: P15375)
[x] Group C: Below 1MB (138: P15376)
[x] Group D: Below 5MB (129 P15382)
[x] Group E: Below 10MB (63 P15381)
[x] Group F: Below 50MB (132: P15379)
[] Group G: Below 100MB (48 P15377)
[] Group H: Below 1GB (79: P15378)
[] Group I: The rest (reading-web-team, wmfall, arbcom-l, wmfsf, wikinews-pl, wikimedia-in-exec, daily-article-l)
Mailing lists can go up (volunteer to be done sooner) or go down due to possible complexities of encoding issues in the archive if they are old.
The script to migrate mailing lists will first send an email to admins of that mailing list saying it's going to be disabled, then disable the mailing list, migrate it and then migrate the archive and at last index the archive for search and then send the "congratulation upgrade is finished" email to the admins again.
Links to mailing list pages and subscriptions will change and once it's all done, private archives won't be accessible in their old place anymore (and possibly will be deleted) but they will be retained in hyperkitty (An example: https://lists-next.wikimedia.org/hyperkitty/list/wikitech-l@lists-next.wikimedia.org/thread/CTYPGVR22FOHDFZOZ3RGNQNL34MIRS5S/) archives of public mailing lists will be kept in both old and new places.