[MM3-users] How to enable VERP?

Hi,

I'm a little confused as to how to enable VERP. mailman3 Debian package, version 3.3.3-1, using Exim 4 MTA.

In /etc/mailman3/mailman.cfg I added:

[mailman]
…
verp_delivery_interval: 1
verp_probes: yes

and restarted mailman3.service.

The list's "Alter Messages / Personalize" setting is "Individual" (but I tried "Full" as well and saw no difference in VERP behaviour).

I can see the MTA is doing an individual delivery for each recipient, and the list's custom footer tells the recipient which address they are subscribed under, so I know that part is working.

With VERP enabled I was expecting the Return-Path header in the delivered list mail to include a cookie to identify the individual subscriber, but instead it is "listname-bounces@example.com" like always.

In mailman.cfg my MTA-related settings are:

[mta]
incoming: mailman.mta.exim4.LMTP
outgoing: mailman.mta.deliver.deliver
smtp_host: localhost
smtp_port: 25
configuration: python:mailman.config.exim4

And the Exim configuration itself has ther macros, router and transport files from the "Exim" section of here:

https://docs.mailman3.org/en/latest/config-core.html#configuring-mta

edited only for correct paths.

That's been working for months for delivering list email in and out, but I'm just now trying to enable VERP and it's not happening.

Is there something I'm missing?

Thanks, Andy