We have upgraded to the latest version of the Mailman software that has some features specifically applied to deal with the DMARC issue ISP's have put in place previously announced.
We suggest logging into your mailing list administration area and making changes to take advantage of these changes. Our suggested settings are as follows:
General Options Area:
Replace the From: header address with the list's posting address to mitigate issues stemming from the original From: domain's DMARC or similar policies. - NO
Hide the sender of a message, replacing it with the list address (Removes From, Sender and Reply-To fields) = NO
Privacy Options>Sender Filters Area: Action to take when anyone posts to the list from a domain with a DMARC Reject/Quarantine Policy = Munge From
Shall the above dmarc_moderation_action apply to messages From: domains with DMARC p=quarantine as well as p=reject = YES