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Why Are My Emails to Hotmail Failing With Error 451 4.7.650 Right Now?
Microsoft’s email servers are currently experiencing widespread delivery issues that incorrectly reject legitimate emails sent to Hotmail, Outlook, and Live accounts. Administrators receive a specific rate-limiting error code despite maintaining excellent IP reputations.
Delivery Disruptions
Email administrators rely on stable communication channels to maintain daily business operations. Multiple IT professionals reported massive delivery failures specifically targeting Microsoft-managed domains on February 25, 2026. These ongoing disruptions are affecting corporate environments and enterprise platforms like Hornet Security across various global regions.
Understanding the Error
System administrators currently encounter a specific bounce message indicating their server has been temporarily rate limited due to IP reputation. The status code 451 4.7.650 implies that Microsoft’s inbound filtering system has restricted the sender’s IP address capacity. However, diagnostic services like MX Toolbox show zero blacklist entries and completely clean server sending histories for these affected domains.
Identifying the Cause
Recent updates to Microsoft’s global email screening processes appear to be the root cause of these sudden message rejections. Microsoft has enforced stricter authentication standards, which inadvertently flag highly reputable senders as security risks. The official Microsoft Anti-Spam IP Delist Portal confirms that many affected IPs are neither listed nor blocked, pointing directly to an internal filtering anomaly.
Recommended Actions
You should take a structured approach while Microsoft resolves this internal system behavior.
- Monitor your outgoing SMTP logs closely to identify messages failing with the 451 status code.
- Verify your domain has correctly configured SPF, DKIM, and DMARC records to meet strict 2026 standards.
- Submit your bounce logs through the official Microsoft Postmaster portal to formally log the false positives.
- Communicate these routing delays transparently to your corporate users to manage delivery expectations.