Email server name: {0} Email Server IP address: {1} Technical error message: {2} Fix the problem The firewall administrator ...

Email server name: {0}
Email Server IP address: {1}
Technical error message: {2}

Fix the problem
The firewall administrator needs to open port 25. For more information, see Network ports for clients and mail flow in Exchange 2013. The recipient's email server needs to allow messages from the IP addresses listed in Exchange Online Protection IP addresses.

We'll keep trying to send the message for a total of 48 hours. After 48 hours, the message will expire, and Office 365 will return a non-delivery report (NDR) to the sender.

Opening a support ticket won't resolve this issue because it's due to a problem that's outside the Office 365 service.