Mailman 3 SaaS

How to disable DMARC mitigation without compromising deliverability?

Sometimes running a mailing list in DMARC mitigation mode can be inconvenient. However, disabling it with stock Mailman code is not recommended, as it will likely compromise deliverability.

New IT offers a custom configuration that enables this option safely.

To configure your mailing list for non-DMARC-mitigated but still security-compliant mode:

1. On the “Alter Messages” page in list settings, set Don't break DKIM to “Yes”
2. On the same page, ensure Filter content is set to “No”
3. On the “List Identity” page, ensure the Subject prefix is empty
4. Ensure the list:member:regular:header template is empty (default)
5. Ensure the list:member:regular:footer template is empty (set explicitly in Postorius)
6. Set “DMARC mitigation action” to “No DMARC mitigation”

With this configuration, Mailman reliably preserves DKIM signatures when forwarding messages to list members.