Microsoft are rejecting your mail

November 9th, 2026 by pdw On Friday morning, we became aware that a significant amount of email to Microsoft-run mail systems was being rejected. This included mail to hotmail.com and outlook.com. The messages were being rejected with the following message: 550 5.7.1 Message rejected: Message lacks SPF/DKIM/DMARC Auth Records We checked our logs, and found that we’d seen this message over 500 times on Thursday, but not once before that. The affected messages all had completely valid SPF and DKIM, but did not have a DMARC record. We added a DMARC record with a “none” policy to some of the affected domains, and sure enough, mail was then accepted again. A quick fedi-survey confirmed that we were not alone. We don’t normally re-use blog…