Exchange online error during connectors work with my on-premises email servers

Kelvin Shee 1 Reputation point

hi expert,

I want to setup connectors work with my on-premises email servers.

and in my exchange Connectors I hit error for RecipientStatus:[{LED=550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup};{MSG=};{FQDN=};{IP=};{LRT=}]


attached with the error message log.

can someone help me, how I can solve this issue?


Microsoft Exchange Online
Office Management
Office Management
Office: A suite of Microsoft productivity software that supports common business tasks, including word processing, email, presentations, and data management and analysis.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Aholic Liang-MSFT 13,821 Reputation points Microsoft Vendor

    Hi @ Kelvin Shee,

    Just wondering if you created a remote mailbox on-premises for this recipient?

    This issue occurs if the user was created in Microsoft 365 and the on-premises Exchange environment doesn't have objects for the user to reference.


    You can refer to this link to create a remote mailbox on-prem, and then test whether sending mail is successful after directory synchronization:

    NDR error 550 5.1.10 RESOLVER.ADR.RecipientNotFound - Exchange | Microsoft Learn

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