Hello, I have sent up an exchange server for a trading company about 2 years, It is normal. But my client told me he can't send to an email address, like xx@xxxxxxxxxxx recently. The undelivery message is " Unable to deliver message to the following recipients, due to being unable to connect successfully to the destination mail server. ? " I can telnet to his smtp port 25, and send test email for him rather use linux send email. Anyone have solutions please help me. Ths, : ) Kenny