We haven't been able to deliver the message to the recipient yet. When we tried delivering the message, we couldn't connect ...

We haven't been able to deliver the message to the recipient yet. When we tried delivering the message, we couldn't connect to your organization's email server or it responded with a temporary error. Please review these details:

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

Because this is an error with the recipient's domain, you'll need to contact them another way until they solve the problem. Unfortunately, Office 365 support won't be able to solve the problem because the problem is on the recipient's domain, not yours.