Outlook.com bounces legit emails as Microsoft's authentication crackdown goes sideways
Missing DMARC or wobbly SPF means your mail may be treated as suspicious
Outlook.com is experiencing difficulties accepting legitimate emails due to Microsoft's recent authentication crackdown. The issue seems widespread, with affected users encountering problems such as non-delivery reports due to SPF validation failures and a lack of DMARC information. The troubles began at the end of last week and are believed to be a result of Microsoft tightening email acceptance rules.
If a domain lacks proper SPF or has a missing DMARC record, Outlook.com treats it as suspicious and refuses to accept emails. These rules were designed to combat spam and bulk senders, but small senders appear to be impacted. Microsoft announced new rules in 2025, requiring DMARC, SPF, and DKIM compliance for domains sending over 5,000 emails per day.
However, small senders are now experiencing issues, even with compliant settings. Microsoft has not issued any advisory to customers explaining the rule changes. The company is actively investigating the cause of the email delivery issue, with engineering teams analyzing service telemetry and customer-provided data.
Written by urgent.news from The Register Science's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
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