We haven't been able to deliver it to the recipient yet because we can't connect to your organization's on-premises email server. Based on the error we received, it looks like your on-premises server isn't available to receive email. Please review these details:
Recipient: {Recipient}
Email server name: {DestinationMailServer}
Email server IP address: {DestinationIP}
Connector name: {ConnectorName}
Technical error message: {MessageDetail}
To fix the problem, make sure that the above email sever available. If your organization is using Microsoft Exchange, you can follow the steps in the following article: A Network Error Occurred while Communicating with Remote Host
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.
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We haven't been able to deliver it to the recipient yet because we can't connect to your organization's on-premises email ...
We haven't been able to deliver the message to the recipient yet because we can't connect to the recipient email server. ...
We haven't been able to deliver the message to the recipient yet due to a problem on your organization's email server. Validation ...
We haven't been able to deliver the message to the recipient yet. It looks like your remote server's firewall is blocking ...
We haven't been able to deliver the message to the recipient yet. Office 365 received an error because validation failed ...