I am using DDNS for my “DNS”. The Exchange 2000 server is able to sent mail but cannot receive external mail.
Below is the error message tested from a web email client by replying the email any idea?
he following addresses had permanent fatal errors
(reason: 550 User unknown)
Transcript of session follows
… while talking to mx1.mailhop.org.:
< << 550 User unknown
550 5.1.1 … User unknown
< << 503 valid RCPT command must precede DATA
Have done the following
1) Check the DNS settings
2) Check the SMTP port 25 by telnet