We are using Exchange 5.5 and are being told by some customers that they will not accept our e-mail because our server is not RFC 1123 compliant and responds to the SMTP HELO command without a fully qualified domain name (FQDN). Our server responds with only its name: exchange_server. How do we get the Exchange server to respond with an FQDN?
You'll want to make sure a PTR record exists in your public DNS record pointing to the public IP address associated with the Exchange 5.5 server's Internet Mail Service (IMS). This should do the trick for you. The IMS gets the name that it's publishing in the received and message tracking headers from the PTR record.
If for some reason that's not a valid option for you, you should be able to change the primary DNS suffix on the external-facing NIC of the Exchange 5.5 server to reflect the public DNS namespace. This requires a reboot.
Hope that helps!
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