An external user sends an email to multiple recipients in the organization. However, no one received the email. When looking at the logs, it shows the error: SMTP error from remote mail server after sending data block: 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup. In this article, you will learn how to fix 550 5.1.10 RESOLVER.ADR.RecipientNotFound in Exchange Server.
550 5.1.10 RESOLVER.ADR.RecipientNotFound error
The Recipient Filter agent is an anti-spam feature that blocks inbound emails addressed to recipients that don’t exist in your organization’s directory. It checks incoming SMTP connections and rejects messages destined for invalid/non-existent mailboxes. This is done before the message is even fully accepted, which saves bandwidth and reduces spam processing overhead.
However, if an external sender sends an email to multiple recipients in the organization, and one of the email addresses is incorrect or doesn’t exist, the email will not be delivered to anyone. This includes the valid recipients. That’s the problem.
When you send an email to multiple recipients, it should be delivered to the valid addresses, while only the invalid ones should fail.
Fix 550 5.1.10 RESOLVER.ADR.RecipientNotFound error
To fix the 550 5.1.10 RESOLVER.ADR.RecipientNotFound error in Exchange Server, follow the steps below:
- Run Exchange Management Shell.
- Change the directory to the Exchange installation scripts folder.
cd $env:ExchangeInstallPath\Scripts\- Uninstall the anti-spam agents. This will remove the following anti-spam agents:
- Content Filter Agent
- Sender Id Agent
- Sender Filter Agent
- Recipient Filter Agent
- Protocol Analysis Agent
.\uninstall-AntispamAgents.ps1- Disable the recipient validation.
Set-RecipientFilterConfig -RecipientValidationEnabled $false- Restart the Microsoft Exchange Transport Service.
Restart-Service MSExchangeTransportVerify your work
Always verify that everything is set correctly after applying the above changes.
Run the Get-TransportAgent cmdlet.
Get-TransportAgent The output should not show the Recipient Filter Agent in the list.
Identity Enabled Priority
-------- ------- --------
Transport Rule Agent True 1
DLP Policy Agent True 2
Retention Policy Agent True 3
Supervisory Review Agent True 4
Malware Agent True 5
Text Messaging Routing Agent True 6
Text Messaging Delivery Agent True 7
System Probe Drop Smtp Agent True 8
System Probe Drop Routing Agent True 9Run the Get-RecipientFilterConfig cmdlet.
Get-RecipientFilterConfigThe output shows the RecipientValidationEnabled property as False.
RunspaceId : a58de183-7b46-438d-823f-3c23637cfcf2
Name : RecipientFilterConfig
BlockedRecipients : {}
RecipientValidationEnabled : False
BlockListEnabled : False
Enabled : True
ExternalMailEnabled : True
InternalMailEnabled : FalseWhen an external sender emails multiple recipients in your organization, the message is delivered to all valid addresses. If one of the addresses is incorrect, only that address will be rejected, and the others will still receive the email.
That’s it!
Read more: Exchange Server health check with PowerShell script »
Conclusion
You learned how to fix 550 5.1.10 RESOLVER.ADR.RecipientNotFound error in Exchange Server. The solution is to uninstall the anti-spam agents, disable the recipient validation, and restart the transport service. After that, emails will be delivered successfully to the valid recipients in the organization.
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