I have had this issue for a while now. I have tried to resolve it a number of ways and no luck. The error is a #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##. It only occurs with appointments from one user. We are on Exchange 2007 SP1 but the user account has existed since Exchange 5.5 and originally had a username of firstname@domain.com. The current user name is firstinitiallastname@domain.com. This address works fine. I recieve a IMCEAEX- O=Organization OU=Group cn=Recipients cn=firstname@domain.comI have added this x500 address as a proxy on the users address list. The email address that errors is not the same as the legacyDN value. The legacyDN value is O=Organization OU=Group cn=Recipients cn=firstinitiallastname with no domain suffix.Have deleted the nickname cache on all machines multiple times. Still occurs.This only occurs on replies to appointments. It does not occur on replies to emails. Should the legacyDN value be changed to reflect the address in the error? will this screw up anything else?

Hi,Did you also tried to have a look with MFCMapi, we once had a strange issue where a user which does not exist anymore still was listed as a delegate. The only way to solve this was by using MFCMapi. Have a look at the following newsgroup post:http://groups.google.com/group/microsoft.public.windows.server.sbs/browse_thread/thread/b9ab6aa5a7b4f30f/1be35a76c38db7b5?hl=nl&ie=UTF-8&oe=UTF-8&q=mfcmapi+and+delegateRegards,Johanblog: www.johanveldhuis.nl