HI, My mail server has been unable to send mails to a domain. It esatblishes the SMTP connection with the mail server and then it is being dropped by destination server. I get the message "Unable to send as the sender's domain does not resolve" - 451. In MS KB, it has been attributed to Reverse Look up by the destination server. Means, the destination server resolves the FQDN against the IP Address. I have got a subdomain under my ISP and that obviously is not registered with InterNIC. I am running one DNS server at my end and it has been configured with a reverse Zone. My ISP is not ready to listen. Is there a way, which I can get to the domain's mail server, by? Regards, Chand Deshwal (M.Tech CS&E, MCSE, CCNA) Network Administrator Kampsax India Ltd., Gurgaon ph: +91 124 6348259-62, Extn. 712 chand@xxxxxxxxxxxxxxxxx <mailto:chand@xxxxxxxxxxxxxxxxx> http://www.kampsaxindia.com <http://www.kampsaxindia.com/>