It's the exact same problem as the other mailop thread "Outlook.com:
intermittent DKIM failures".
It's not you, it's them.
- Mark Alley
On 6/20/2025 3:36 PM, Mark Fletcher via mailop wrote:
Hi All,
We're seeing instances of emails being rejected by Microsoft with DKIM
errors, and I have no idea why. It's happening to maybe 1% of the
email we send to Microsoft properties (outlook.com
<http://outlook.com>, hotmail.com <http://hotmail.com>, live.com
<http://live.com>, etc). The error we get is:
550 5.7.515 Access denied, sending domain GROUPS.IO <http://GROUPS.IO>
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=
Fail , DMARC= Pass
These are email group messages. We re-write the From line for all of
them, so they all have the @groups.io domain. For a given list
message, if it fails for one Microsoft recipient, it fails for all of
them.
I dump out these emails and run two different DKIM signature check
programs on them, and they pass.
Does anyone have any suggestions for things I should check?
Thanks,
Mark
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