Microsoft Bounces Legitimate Email Since Nov. 5 as DMARC Checks Hit Small Senders
Updated
Updated · Computerworld · Nov 10
Microsoft Bounces Legitimate Email Since Nov. 5 as DMARC Checks Hit Small Senders
3 articles · Updated · Computerworld · Nov 10
Summary
Mail to Outlook, Hotmail, Live and MSN has been intermittently rejected since Nov. 5, with legitimate messages bouncing even from ordinary domains that are not bulk senders.
550 5.7.1 and 550 5.7.23 errors point to missing DMARC, SPF or DKIM, but Microsoft has issued no policy notice and some affected domains reportedly already have all three configured.
Microsoft forum moderators described the problem as a service degradation under investigation, while analysts said it could reflect both a policy shift and a bug in enforcement.
MailRoute said a basic DMARC TXT record — "v=DMARC1; p=none" — can stop the bounces for domains missing one, and organizations should check logs and resend time-sensitive mail.
The glitch highlights a broader shift toward universal email authentication: Microsoft required DMARC for senders above 5,000 daily messages in May 2025, and experts expect stricter enforcement to spread to all senders.