Outlook.com rejects email from domains without DMARC
The gist
Microsoft's Outlook.com, Hotmail, Live and MSN are rejecting some mail from domains without DMARC records.
Senders with correct settings also report blocks, and Microsoft has confirmed no cause.
How it unfolded
- May 5, 2025Microsoft begins enforcing bulk sender requirements on live.com, hotmail.com and outlook.com; non-compliant bulk email from domains sending over 5,000 messages a day is rejected with 550 5.7.515 Access denied.
- Nov 4, 2026A user reports intermittent rejections from multiple senders, including Google and Zoho, on two separate personal Outlook.com accounts.
- Nov 5, 2026MailRoute first sees the bounces in its own outbound logs; public reports from other administrators appear the same day. A Zoho sender's email is rejected at 15:50 and arrives when resent at 16:09.
Key terms
- DMARC
- An email authentication protocol that lets domain owners protect their domain from unauthorized use such as spoofing and phishing.
- SPF
- An email authentication method that checks whether a sending mail server is authorized to send mail for the sender's domain.
- DKIM
- An email authentication method that uses a digital signature to let a domain claim responsibility for a message and detect tampering.
Source: Wikipedia