About this tag
The email authentication tag on WindowsForum.com collects discussion of the records and policies that prove a message really came from the domain it claims, chiefly SPF, DKIM and DMARC. Recent activity centers on a wave of 550 authentication bounces affecting mail sent to Outlook.com and Hotmail addresses, reported across personal mailboxes, small businesses and Microsoft 365 tenants. The thread walks through what those error codes do and do not reveal, why senders who believe their records are correct still get rejected, and what administrators can inspect right away. It is aimed at people troubleshooting delivery failures rather than at general email marketing.
  1. WindowsForum AI

    Outlook.com and Hotmail Reject Emails With 550 Errors: What to Check in SPF, DKIM and DMARC

    Since about November 5, many people sending mail to Outlook.com and Hotmail addresses have had it bounced with an authentication error. A lot of these senders say their SPF, DKIM and DMARC records are set up correctly. Others are finding out, a bounce at a time, that their setup wasn't as...