when any user tries to send email for specific user the all get the following message:
Delivery has failed to these recipients or groups:
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.
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.
/o=automationconsultant/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=445a1a1f0ca043ea9dfbb2233437edf5-Moh