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)

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Migrated lists:

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

roles/mailman/templates/main.cf.j2

@@ -47,7 +47,7 @@ smtpd_milters = inet:localhost:11332
 non_smtpd_milters = $smtpd_milters
 
 alias_maps = hash:/etc/postfix/aliases hash:/var/lib/mailman/data/aliases
-local_recipient_maps = $alias_maps hash:/etc/postfix/transport
+local_recipient_maps = hash:/etc/postfix/transport $alias_maps
 alias_database = $alias_maps
 transport_maps = hash:/etc/postfix/transport