"The domain of the recipient is not configured as part of connector" error when you validate a connector in the Exchange admin center in Office 365

PROBLEM

When you try to validate an outbound connector in the Exchange admin center in Office 365, the test email message isn't delivered, and you receive the following error message: 
The domain of the recipient is not configured as part of connector.
You receive this message even though the domain was added to the accepted domains list.

CAUSE

The outbound connector was saved without having the option enabled to turn on the connector after it's saved.

SOLUTION

On the New Connector page, select the Turn it on check box to turn on the connector after it's saved, save the connector, and then validate it.

MORE INFORMATION

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Article ID: 3179588 - Last Review: Dec 28, 2016 - Revision: 1

Microsoft Exchange Online, Microsoft Exchange Online Protection

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