[Mailman-Users] List posts sent to AOL list subscribers bounce as undeliverable (v. 2.1.20)

[John Levine]

>The issue is that list posts sent to AOL subscriber addresses are now bouncing as undeliverable with the bounce code: "521
>5.2.1 :  AOL will not accept delivery of this message."

I see that you have a yahoo.com address.  If there's a yahoo.com
address on the From: line of the list mail, AOL and Yahoo's well
documented abuse of DMARC will cause the failure you're seeing.

If you're running a recent version of Mailman, there are some DMARC
workarounds you can use.  Other than that, I'd find a different
address to mail from, not at Yahoo, not at AOL, and preferably not at
Gmail.

R's,
John