On Tue, 12 May 2026, Fernando MM wrote:
As others have mentioned, this is a long-standing issue with Outlook.com
that seems to be related to internal DNS timeouts.
After some experiementation I can say it's more than that. I tweaked my
MTA setting so if it gets that 5.7.515 response, it requeues the message
up to three times.
I found that if a message is rejected once, it'll be rejected every time.
We send lots of messages to the address that's failing, with most of them
succeeding, frequently within a few seconds of a rejection. I have looked
at the messages and cannot see any obvious difference between the ones
that work and the ones that are rejected. They're all plain text, no
MIME. They all happen to have a lot of other addresses on the To: line,
and everyone else delivers them without trouble so I am quite sure that
despite what Outlook says, the DKIM signature is OK.
R's,
John
On Fri, May 8, 2026 at 4:13 PM John Levine via mailop <[email protected]>
wrote:
Here's a summary of an SMTP rejection from Microsoft. I am quite sure
that the message had a valid arxiv.org DKIM signature and was sent
from an address in the SPF record. Anything I can do about it?
We've been sending this person mail for years at an outlook.com.au
address and nearly all of them have worked, including several today.
550,5.7.515,Access denied, sending domain ARXIV.ORG 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 [SY8P300MB0731.AUSP300.PROD.OUTLOOK.COM
2026-05-08T18:21:38.150Z 08DEAD0640C37A36] [
MW4PR04CA0059.namprd04.prod.outlook.com 2026-05-08T18:21:38.232Z
08DEACE91EBF534A] [MW1PEPF0001615B.namprd21.prod.outlook.com
2026-05-08T18:21:38.253Z 08DEACF5EA686851]
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