There were a few previous issues discussing DMARC and mailing lists. Creating a new issue to capture current state and propose a DMARC compatible default setting for lists.wikimedia.org. Will try to include related issues, apologies in advance if I miss any.
Our current mailman version (2.1.18) supports DMARC sender filters which can conditionally modify a message for re-mailing in a DMARC compatible way. This can improve deliverability of messages from users of lists.wikimedia.org who have strict DMARC policies set by their email provider. However, these appear to be largely disabled today (although they can be optionally enabled by list admins on a per-list basis).
Proposing a setting of DEFAULT_DMARC_MODERATION_ACTION=1 (Munge From). This would by default rewrite (Munge) the From: header with the posters name 'via the list' and the list's address and merge the poster's address into Reply-To: for messages whose original From: domain publishes a DMARC policy of p=reject or p=quarantine. Additional options are outlined in detail at https://wiki.list.org/DEV/DMARC
- Improve message delivery for lists.wikimedia.org users sending from DMARC enabled addresses.
- Only modify messages that may have delivery issues if unmodified.
- List administrators could still choose a different setting (as long as it has a higher value).
- Additional overhead (DNS lookups, rewrites)
- Change in behavior. Users may wonder why sender addresses and reply-to are different.
- Inconsistent behavior. Depending on DMARC policy some messages would be from the original sender address, others from the list address.