If mail to an Outlook.com or Hotmail address is rejected, keep the full non-delivery report. The exact error, sending IP and sending service matter; “Microsoft blocked us” is not enough to choose a remedy.
Identify the actual rejection
Record the SMTP code, affected recipients and when it started. Keep private message content out of public support posts. A temporary rate limit, a policy rejection and an invalid recipient need different responses.
Ask the sending provider to investigate
The provider may need to inspect authentication, sending patterns and IP reputation. On shared infrastructure, the person controlling the sending IP may need to act. Do not assume the age of your domain proves its mail cannot be rejected.
Use the right Microsoft support route
Microsoft publishes sender troubleshooting for Outlook.com. Follow the process that matches the actual service and error. Microsoft 365 organisation mail and consumer Outlook.com mail do not necessarily use the same review route.
Fix the cause before requesting another review
A review request does not guarantee delisting or delivery. Do not submit repeated requests without investigating the rejection, or pay an unfamiliar site that promises to remove every block.
For configuration help, see email security and deliverability.
Sources and further reading
Guidance checked 26 October 2026: Microsoft’s Outlook.com sender troubleshooting.