Thank you Stephen and Odhiambo for your advise on this.
Kind regards, Prasanth
On Tue, 14 Apr 2026 at 16:06, Stephen J. Turnbull <steve@turnbull.jp> wrote:
Washington Odhiambo via Mailman-users writes:
[...] (see his mail)
I don't have specific comments beyond Odhiambo's excellent suggestions.
For the host -> host migration, if you are very concerned about a high-quality migration and can afford the effort, I would emphasize starting with a duplicate of the working host as close as possible, then reviewing configurations and eliminating weak points, general improvement, and optimization of the system while keeping a working configuration after each stage. However, unless you are considering changing MTAs (including a major version upgrade with backward incompatibilities), I don't recall people having problems with this.
For the host -> containerized transition, there's not a lot of lore about this. As far as I know, the Mailman side doesn't present problems, but for those not experienced with containers, networking and persistent storage configuration can cause issues.
For minimal downtime, I have done a 5k list migration from Mailman 2 to Mailman 3 with zero downtime of post distribution. If there are large archives, then archive migration will take time, just no way around that (although you can keep the old archives online). The basic strategy is to note that routing to lists in the MTA has some prioritization when different routes might apply to a particular destination address, then arrange that the "new" host gets the posts as each list is created, while the old host continues to handle the old posts.
That approach had the advantage in that case both Mailman hosts were dedicated to Mailman. Also, for a 5k list installation with Postfix, I needed a small change to routing. Mailman normally creates a hash db, which takes a lot of time (seconds) with a lot of lists. To get~ zero downtime (ie, less than than normal relay delays in Postfix), I created an alternative routing mechanism that talks directly to PostgreSQL. I think you don't need to do that with Exim4, can't help with other MTAs.
Regards, Steve
-- GNU Mailman consultant (installation, migration, customization) Sirius Open Source https://www.siriusopensource.com/ Software systems consulting in Europe, North America, and Japan