Setup mailman3 server

We want to migrate to mailman3 as mailman2 is basically unmaintained and requires Python 2 which is EOL.

Because the mailman and mailman3 packages conflict and we don't want to perform a big bang migration, mailman3 must be deployed on a separate server. mailman-web (mailman3's web interface) hasn't been packaged yet, so for now we are using my homebrewed PKGBUILD.

[1] https://gist.github.com/klausenbusk/5982063f95c503754a51ed2fefb8915e

Ref #59 (closed)

---

Migrated lists:

• arch-announce
• arch-devops-private
• arch-events
• arch-wiki-admins

roles/mailman3/templates/settings.py.j2

@@ -7,7 +7,7 @@ from mailman_web.settings.mailman import *
 
 #: Default list of admins who receive the emails from error logging.
 ADMINS = (
-    ('Mailman Suite Admin', 'root@localhost'),
+    ('Mailman Suite Admin', 'root@{{ lists_domain }}'),
 )
 
 # Postgresql datbase setup.
@@ -41,3 +41,7 @@ MAILMAN_REST_API_PASS = '{{ vault_mailman_admin_pass }}'
 EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'
 EMAIL_HOST = '{{ hostvars['lists.archlinux.org']['wireguard_address'] }}'
 EMAIL_PORT = 25
+
+#: Sender in Emails sent out by Postorius.
+DEFAULT_FROM_EMAIL = 'postorius@{{ lists_domain }}'
+SERVER_EMAIL = 'root@{{ lists_domain }}'