I have an end user who sometimes receives bounce-back emails when sending to a workmate. However the intended recipient does receive the original email.

Both users are on the same Exchange 2010 server. Does anyone know how to resolve this issue?

From: Microsoft Outlook 
Sent: Tuesday, 21 February 2012 9:18 AM
To: Joe Smith
Subject: Undeliverable: 

Delivery has failed to these recipients or groups:

Frank Spencer
The email address that you entered couldn't be found. Check the address and try 
resending the message. If the problem continues, please contact your helpdesk.

Diagnostic information for administrators:

Generating server: server.domain.local

#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

Original message headers:

Received: from server.domain.local ([fe80::3264:c532:29f2:fc75])
by server.domain.local ([fe80::32b4:c582:29f2:fc75%17]) with mapi
id 14.01.0355.002; Tue, 21 Feb 2012 09:17:30 +1100

Does this happen with all users or just one user? Does this happen when they are sending to a specific workmates or to all other workmates? More information on your troubleshooting steps would help narrow down an answer. I will however offer a solution since I have seen this error message before.

I had this issue with some of my clients and this is how I resolved it:

Are they using auto-complete to select the recipients address? Have them try to type the email in manually. If this works correctly then I would delete their .n2k file under their profile. Sometimes the .n2k file can be corrupted and needs to be cleared out. Lets hope they are not using it for an address book.

You don't say what version of Windows but the .n2k file is genearlly stored at the following paths.

Windows XP:

Drive:\Documents and Settings\Username\Application Data\Microsoft\Outlook

Windows 7:


  • Thanks for your help. I think a corrupt address entry in the N2K file is the answer. I have asked the user to delete the address from the To: drop-down to test. – Ash Feb 23 '12 at 1:14

We encountered the same issue when we removed a few of our distribution groups from AD and re-created them with the same name/e-mail address so they would sync with Office 365. Auto-complete was referencing the id associated with the old object and the user would receive a #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## error . Having the user type out the entire address once seemed to correct the issue and update the .n2k file.


I found this was NOT to do with the N2k file

It was because I removed the mail box from Exchange server (2007) before I removed them from the groups is the DSA.MSC on one of the DC's.

If you have this for a user in a group re-add them to the groups, give them a mail box, then remove from the groups and DISABLE (remove the mailbox/exchange properties from the user). Not sure exactly how this would work if the user has already been deleted

then this problem should no longer show

Hope this helps someone


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