The message could not be delivered because we could not connect to the recipient's email server. The sender of the message ...

The message could not be delivered because we could not connect to the recipient's email server. The sender of the message was sent a non-delivery report with details of the problem. Please review these details:

Recipient: {Recipient}
Email server name: {DestinationMailServer}
Technical error message: {MessageDetail}

To fix the problem, we recommend that you check the recipient's email admin about the error.

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

Note, we sent a non-delivery report to the sender that gives the details about why the message couldn't be delivered.