Mailman people --

I've been running mailman3 in production in Google's cloud for about 4 years now.

Recently I started seeing many bounces from members who subscribe from yahoo, aol, bellsouth, or verizon.

The bounces were triggered by DKIM failures. DKIM failures in my setup are apparently not new. Some spelunking revealed I've had outbound DKIM failures for years. It is possible my system has never properly signed outbound emails. But now it matters to these email providers.

I decided to spin up a dev/test instance.

I installed mailman3 from scratch in a venv environment on Debian 12. I used these excellent instructions: https://docs.list.org/en/latest/install/virtualenv.html#virtualenv-install I got this:

GNU Mailman 3.3.10 (Tom Sawyer) Python 3.11.2 (main, Apr 8 2026, 01:58:00) [GCC 12.2.0]

What I learned (relearned from 4 years ago):

• Getting mailman up is easy.
• The hard part is getting traffic in and out. Postfix is complicated to set up in this environment. Getting all the DNS and multiple layers of proxies set up to access Postorius/Django/Gunicorn is not simple.
• I took lots of snapshots along the way. I used those snapshots to back out of a couple of dead ends. Highly recommended.

I have only one open issue. Shortly after I start mailman I get this warning:

/opt/mailman/venv/lib/python3.11/site-packages/falcon/request.py:2483: DeprecatedWarning: The RequestOptions.auto_parse_form_urlencoded option is deprecated. Please use Request.get_media() to consume the submitted URL-encoded form instead. warnings.warn(

I am ignoring this. Is there something I should do about this?

In the end, after experimenting with many possible solutions (including installing openDKIM), the solution was simple. I added this line to my mailman.cfg:

remove_dkim_headers: yes

Once the DKIM headers were removed, my outbound SMTP relay happily signs the emails and all is well. (Or it least it is after hours spent learning how to configure the outbound relay properly.)

Someday soon I need to completely reinstall my production environment, but for now, I'm continuing on.

Thanks to this community for all you do.

-- Stephen Daniel