I have been running exchange for my company for a number of years and can usually sort out most of the problems it throws at me. But just recently I have been asked to add a new domain onto our existing single Exchange 2003 std server as a secondary domain. Our primary email domain which we will call defaultdomain.com has no problems sending or receiving email internally or externally. Our new secondary domain newdomain.com works fine internally and I can send mail out, but when I try and reply or send a new message in I get the following NDR message, This is an automatically generated Delivery Status NotificationDelivery to the following recipient failed permanently: postmaster@newdomain.comTechnical details of permanent failure:PERM_FAILURE: SMTP Error (state 9): 550 5.7.1 Unable to relay for postmaster@newdomain.com Now I have added the new domain to the default recipient policy and waited, then rebooted the server, all my exchange usershave been updated with a new email address for the new domain. Also I have double checked the DNS entrys my ISP has added for my new domain and all the relevant A, RDNS and MX records are inplace.I would be grateful is someone can shed some light on this problem.

If you did an in-place upgrade from exchange 2000 to exchange 2003 then install dotnet framework 1.1. If any other version or updatesofdotnet framework are installed remove them and then install dotnet framework 1.1