MailRoute founder and CEO Thomas A. Johnson wrote on Nov. 6 that Microsoft's consumer mail service has, since Nov. 5, 2026, been turning away some messages from domains that do not publish a DMARC record¹.

He named Outlook.com, Hotmail, Live and MSN as the properties involved and said the pattern shows up for ordinary, low-volume senders, not only the bulk senders covered by Microsoft's published high-volume rules¹.

Those earlier rules, which Johnson dated to May 2025, required domains sending more than 5,000 messages a day to Outlook.com to pass SPF, DKIM and DMARC or receive a 550 5.7.515 denial¹.

The new bounce, he wrote, is 550 5.7.1 with the text that the message lacks SPF, DKIM or DMARC auth records, later including a code AS9031519, and often hits domains that already had working SPF and sometimes DKIM but no DMARC record tying them to the From address¹.

Johnson said Microsoft had published no postmaster notice, blog post or service-health entry about the change as of Nov. 6, and that only some messages from an affected domain bounce, so successful delivery does not prove the domain is in the clear¹.

He said MailRoute first saw the rejections in its own outbound logs on Nov. 5 and that other administrators reported the same day¹.

The company, which sells email security and outbound relay, said the typical fix is a DNS TXT record at _dmarc with v=DMARC1; p=none, which he described as a no-enforcement starting point that does not change how other receivers treat the mail¹.

He added that DMARC still fails unless SPF or DKIM aligns with the From domain, and that Microsoft 365 DKIM signed as onmicrosoft.com does not count until the customer domain is signed¹.

Microsoft's own confirmation or a service-health notice was not in the MailRoute post¹.

Sources

1. mailroute.netOutlook.com Is Quietly Rejecting Email from Domains Without DMARC2:20 PM

Read the original at mailroute.net ↗