Microsoft Incident Resulting in Delivery Issues to M365

Incident Report for Mailjet

Resolved

This incident has been resolved.

Posted Nov 13, 2026 - 19:01 UTC

Monitoring

Microsoft is experiencing an incident causing an increased volume of deferred emails across all M365 regions. The affected responses are returning "451 4.7.500 Temporary server error" and "421 4.3.2 The maximum number of concurrent server connections has exceeded a limit, closing transmission channel". Our teams are actively monitoring the situation. Sending to other email providers is not affected

Posted Nov 13, 2026 - 08:36 UTC