Getting NDR ( Remote Server returned ‘550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found’) for existing User.

when any user tries to send email for specific user the all get the following message:

Delivery has failed to these recipients or groups:

 ‘user name’
The email address you entered couldn’t be found. Please check the recipient’s email address and try to resend the message. If the problem continues, please contact your helpdesk.

Diagnostic information for administrators:

Generating server: Exchange server

Remote Server returned ‘550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found

There are different solution for this problem (personally i prefer the third as some solutions worked for some users and didn’t work for the remaining)

1- Delete the Auto-Complete entery of this single user in the outlook.
By deleting the X next the desired entry.


2- Delete the entire outlook Auto-Complete list.
Go to File, Option, Mail, and then click on the Empty Auto-Complete List button under the Send Messages header.

3- Go to ECP, Recipients, Mailboxes, open the desired user proprieties, under email address you will need to add a new entry of X500 Type (with no dot) and email address that is mentioned in the Diagnostic information for administrators part of the NDR message.


Will be

/o=automationconsultant/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=445a1a1f0ca043ea9dfbb2233437edf5-Moh


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