Mailprotector Delays: Microsoft Office 365 Affecting Mail Flow

System Status

Oct 11, 2022 – 17:42 EDT

Microsoft Office 365 Affecting Mail Flow

Update – Microsoft appears to have changed the Exchange Online perimeter, which may have introduced graylisting behavior. Microsoft’s Exchange Online Advisory EX444758 is believed to be the reason for the changes. The start time of the advisory is 9:40 AM which coincides with email delivery delays appearing in Mailprotector’s logs.

Mailprotector has not changed or altered any email delivery operations. The email delays are the result of Microsoft changing the behavior of the Exchange Online perimeter.

Any domain still impacted by Microsoft’s changes today should implement the Inbound Connector for Mailprotector. The KB article that provides the information to implement the connector is found at

Please configure the Inbound Connector and ensure it is enabled. Mailprotector will update recommendations and documentation to emphasize the importance of using the Inbound Connector. The connector will provide additional trust information to Microsoft and reduce the chances of delaying email.