DMARC and Listserves (Hotmail 16Jun2025 edition)
I get this email error for [email protected]
2025-06-13 15:32:10 xfailed [email protected] host hotmail-com.olc.protection.outlook.com [52.101.40.25] SMTP error from remote mail server after end of data: 550 5.7.515 Access denied, sending domain ATT.NET doesn't meet the required authentication level. The sender's domain in the 5322.From address doesn't meet the authentication requirements defined for the sender. To learn how to fix this see: https://go.microsoft.com/fwlink/p/?linkid=2319303 Spf= Pass , Dkim= Pass , DMARC= None [SJ0PR17MB5706.namprd17.prod.outlook.com 2025-06-13T15:29:39.202Z 08DDA9E46D7E4D67] [PH7P222CA0022.NAMP222.PROD.OUTLOOK.COM 2025-06-13T15:29:39.211Z 08DDAA06AF94BE51] [CY4PEPF0000EE32.namprd05.prod.outlook.com 2025-06-13T15:29:39.226Z 08DDA97245006D8E]
Which seems to say it's a DMARC error.
Which is not unusual for a listserve. We are relaying an author's email to a bunch of other people, and we keep their email address in the From: header (our email address is in the FROM envelope of each email).
Since we are mail-list.com and not the author's ISP/Mailbox Provider, why are we sending something somebody else email and it must be spam.
DMARC is an email server add-on that allows each domain name to publish a DNS record of their's, that allows them to codify what to do if one of their email accounts sends an email from other than their specified IP addresses.
The code words are
None
Quarantine
Reject
And the absence of the DMARC record infers None.
None means we do not have a policy, do whatever you want with that email.
Quarantine means put in Spam folder.
Reject means block at server level - bounce back. We are willing to accept bounce back error messages and fix the problem of people spoofing our email addresses.
So back to the story
I don't see where there are any recent posts from this subscriber.
I reread the SMTP error message, and it says
Access denied, sending domain ATT.NET doesn't meet the required authentication level.
I do see some recent messages from AT&T people, so that seems to match up.
MxToolbox says (about an hour later)
https://mxtoolbox.com/SuperTool.aspx?action=mx%3aATT.NET&run=toolpage
No DMARC Record found
DMARC Quarantine/Reject policy not enabled
Not sure I understand why hotmail is rejecting posts, except they may be rejecting from all domains.
Which if so, I have a workaround for that, we will put the list address as the From: header.
More confusing for the people, but easier for the computers to understand.
Let me tweak a setting and see if that stems the carnage.
So every time a subscriber from ATT.NET posts a message, all Hotmail subscribers get a bounce message. We throttle first, and then remove the hotmail subscriber.
I see a few other domain names, but not many different ones.
ATT.NET
FASTMAIL.COM
HOTMAIL.CO.UK
MSKCC.ORG
OUTLOOK.COM
SBCGLOBAL.NET
Is over a few day time period in mid June 2025.
So Hotmail has been sending back bounce messages on their subscribers, when a fellow listserve subscriber from one of the above domain names posts a message.
Kind of perverse, especially since I'm not seeing where any of those domain names have published DMARC settings.
and that is causing problems for some listserves, as Mail-List.com will temporarily stop sending any message to that subscriber from any domain name, and with more bounces will remove the Hotmail address from the listserve.
I will send an email to [email protected] to let them know what I'm seeing.