Hi there, Thanks for reading. We have two Board members whose addressessometimes can't be found by addy book. Emails bounce with a dorked-up FQDN address instead of a the straightforward, configured SMTP address. I can see the symptom on internal client machines: select the user, double click address for properties and view address shows the unusual FQDN address. Deleting Outlook profile and recreating has fixed the issue for weeks at a time, but same internal users and seeing same NDRs. Any ideas will be greatly appreciated! Bob

One more detail.The NDR address looks like this: IMCEAEX-_O=TOWN+20OF+20MY+20TOWN_OU=MyDomain+2Enet_cn=Recipients_cn=User@MyDomain.gov. That's what appears in offending users' address book (as well as in the NDR) instead of the simple SMTP address referred to at the end of the line!

Hi Bob, The error 5.1.1 means that the recipient address is invalid or does not exist in the directory of the recipient email-system. Please check the x500 addresses (equivalent to the old LegacyExchangeDN) of the users. How to set X500 proxy addresses for Exchange Server 2003 recipients and for Exchange 2000 Server recipients http://support.microsoft.com/default.aspx?scid=kb;EN-US;313324 However, if the issue persists, you mentioned it worked after creating outlook profile. So you could disable Exchange cache mode to test the issue. If it still no luck, please let me know if the issue happened on all senders. Please use the suggestion in following article to verify if you have set LegacyExchangeDN value well. Base on my test, if the value is incorret, the error you mentioned can occur. Understanding the LegacyExchangeDN http://www.msexchange.org/tutorials/Understanding-LegacyExchangeDN.html Please Note: Since the website is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information. If the issue persists,please let me know if you areusing Exchange 5.5 or you migrate from 5.5? Whats your Exchange version? Please note Exchange 5.5 has passed support circle. Hope this helps. Thanks, Elvis