Error #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## on exchange 2010


  • H

    Since a bout a week ago we are getting this error  #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##  on our excahnge 2010. This only happens to selected user and some new users that we created three days ago. We have the latest updates running on our exchange. I have search the whole internet and the solutions are to delete the nk2 files and clear cache but the problem is appear to happen to users that are already been created for months ago and even after the cache is cleared the same errors appears.

    I thank you in advance for your asssitance

    Kind Regards


    Tuesday, September 06, 2011 1:29 PM

All replies

  • Do you have all header of such a mail? I had such an issue once with antispam appliance.
    Regards, Konrad Sagala, MCT, MCSE+M, MCITP: Exchange 2007/2010
    Tuesday, September 06, 2011 1:39 PM
  • Here is the header from the original mail.


    Received: from IQJHBAPP01 ( by IQJHBEX01.iqworld.grp
     ( with Microsoft SMTP Server id; Tue, 6 Sep 2011
     08:09:37 +0200
    Date: Tue, 6 Sep 2011 08:09:43 +0200
    From: IQ Helpdesk <iqhelpdesk@iqgroup.net>
    To: <sgarapo@iqgroup.net>
    Message-ID: <9530362.3551315289383381.JavaMail.SYSTEM@iqjhbex01>
    Subject: Your Request with ID :##803## has been Resolved.
    MIME-Version: 1.0
    Content-Type: multipart/mixed;
    Return-Path: iqhelpdesk@iqgroup.net

    Tuesday, September 06, 2011 1:59 PM
  • Hi Jaco,

    Error 5.1.1 its related to invalid recipients.

    In AD properties we have an option to specify an email address and Exchange mailbox property we have an option specify an email address as primary, Can you check whether both the primary email address and the email address on the AD are same. if not change it

    Also, Open OWA and type in the email address and click ctrl+K and see whether address is resolving for the new account.

    Inform if any issue

    Tuesday, September 06, 2011 2:22 PM
  • Hi Rajkumar

    I have checked and the mail adresses are the same in AD and exchange. I have also done the OWA test as asked and checked with outlook running not in cache mode and they find the users.

    The wierd thing is that the problem is intemittend as a gets send then the next minute it gives the error.

    Any other ideas?

    Tuesday, September 06, 2011 2:29 PM
  • The wierd thing is that the problem is intemittend as a gets send then the next minute it gives the error.

    Hi Jaco,

    Do you mean the problem will also be occured intermittend even if you send mails to selected user and some new users using OWA?

    Please post the full NDR message(#550 5.1.1 RESOLVER.ADR.ExRecipNotFound) here.

    Did you migrate from Exchange 2007 to Exchange 2010?

    Please also check whether there is any error event in the Event Viewer on the Exchange server.

    Frank Wang

    Thursday, September 08, 2011 3:02 AM
  • Hi Jaco,

    Any updates?

    Frank Wang

    Monday, September 12, 2011 1:35 AM