Hello all, We are using exchange 2003 FE and BE server. I have a client could not send us an email. Here is the error message below: The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'xxx@xxxxxxx'. Subject 'test ', Account: 'xxx.xxxx.xxx', Server: 'smtp.xxxx.xxx', Protocol: SMTP, Server Response: '550 5.7.1 <xxx@xxxxxxx>... Relaying denied. IP name lookup failed [xxx.xxx.xxx.xxx]', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79 Any idea? Thank you Sam