Microsoft has made a major change to Outlook.com, rejecting some email from sending domains that don’t have a DMARC record.

Domain-based Message Authentication, Reporting and Conformance (DMARC) is another layer that helps authenticate email messages. DMARC tells a server how to handle an incoming email if Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) authentication fails.

Starting Nov. 5, and with no previous notice, Microsoft started enforcing a DMARC requirement, rejecting some email to Outlook.com, Hotmail, Live and MSN addresses from domains without a DMARC record.

MXRoute , the popular email service, sent the following notice to its customers:

Hello,

Within the last 24 hours, Microsoft began enforcing a new rule that rejects some email sent to Outlook.com, Hotmail, Live, and MSN addresses when the sending domain does not have a DMARC record.

We received no advance warning.…