Recoverable error.
SMTP has evaluated all the possible MX records for the host and eliminated all the necessary hosts with a lower preference than this SMTP server. After this processing, SMTP did not have any MX records remaining for this host and did not know where to deliver the mail. This is a configuration error in either SMTP or the domain name server.
The mail is rejected. SMTP continues.
Determine what MX records are stored in the domain name server and why SMTP cannot determine the final recipient. Tell the domain name server administrator about the error.
SMTPRES
ProcessRQR