I have exchange server 2010 and based server is windows server 2008 R2.
450 4.1.8 <user@mydomain.com>: Sender address rejected: Domain not found ) error to some domains. I can successfully nslookup to that domain .my smtpsend log shows 450 4.1.8 <user@mydomain.com>: Sender address rejected: Domain not found . please advice .. thank you.