Hello,

I am glad you asked these questions, as this can help anyone who will later wish to use the dynamic sublists feature for team collaboration when it is merged into Mailman 3.

What does your suggested implementation look like? Would it be something

like main+sub-topic@example.com which would create a sub list called “sub-topic” with inherited permissions from “main”?

Your guess is actually very close because a user will send a mail to a special alias, in your case main-new@example.com (with the -new command as a suffix to the parent list main@example.com). Then Mailman takes the message-ID, generates a database serial number, and using Base32 encoding generates a unique address for the child list (e.g., main-ab@example.com). And indeed because the child list is linked in the database via the parent_id, it inherits its settings from the parent list itself.

What would that bring on top of including [sub-topic] in the subject or

body?

It reduces inbox flooding :)

When you use a subject tag on a mailing list it still follows the broadcast model; if a specific thread for troubleshooting or a specific project gets more replies, every single person on the main list will receive that many emails regardless of whether it was relevant to them or not. And thus, dynamic sublists is an opt-in thread model; the -new email is broadcast both to the main list (main@example.com) and the newly made child list ( main-ab@example.com). Mailman will send a separate announcement to the main list containing the -join and -leave addresses for the new child list.

Also, the creator is automatically subscribed to the new child list and anyone else who is interested can opt-in. All the incoming replies from then on are routed to the child list.

I’m glad our little exchange on the MM3 list was helpful. A great example of the power of searchable archives of such exchanges.

Indeed :D Thanks again!

Regards

Archie

On Fri, Aug 7, 2026 at 4:55 PM Rodrigo Camacho <rodrigo@vitz.fr> wrote:

...

On 7 Aug 2026, at 13:09, Archie Singh <archie.singh2610@gmail.com> wrote:

I am Archie, a Google Summer of Code contributor for GNU Mailman and I am working on implementing Dynamic Sublists, a type of conversation/thread model into MM3.

This sounds like a way to group a set of threads together through a dynamically created list. Today a similar result can be obtained (and often is) by adding something like [UNIQUE ID OF TOPIC] to the subject or even the body of a set of threads sent to one list.

What does your suggested implementation look like? Would it be something like main+sub-topic@example.com which would create a sub list called “sub-topic” with inherited permissions from “main”? What would that bring on top of including [sub-topic] in the subject or body?

...

I wanted to let you know that your entire discussion thread was something I wrote a blog about to explain (dated: 5th May 2026, https://archiegnumailman.hashnode.dev/a-foundational-approach-to-replacing-s...) one of the use-cases of dynamic sublists and in fact if this feature was present earlier in Mailman 3 you would have been able to utilize it for your work :D

I’m glad our little exchange on the MM3 list was helpful. A great example of the power of searchable archives of such exchanges.