Email server name: {0} Email server IP address: {1} Connector name: {2} Technical error message: {3} Fix the problem Your ...

Email server name: {0}
Email server IP address: {1}
Connector name: {2}
Technical error message: {3}

Fix the problem
Your firewall administrator needs to open port 25. For more information, see Network ports for clients and mail flow in Exchange 2013. You need 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 that, Office 365 will stop trying to send the message and will return a non-delivery report (NDR) to the sender.