Undeliverable mail - 554 5.7.1 relay access denied

GWIA configured to relay to another host for outbound messages:
Properties of GWIA | SMTP/MIME Settings | Relay Host for outbound messages
GWIA unable to send emails. Undeliverable mail - 554 5.7.1 relay access denied

GWIA logs show the following:
19:34:51 B021 MSG 422779 Recipient: user@domain.com
19:34:57 B029 DMN: MSG 422779 Send Failure: 554 5.7.1 <user@domain.com>: Relay access denied
19:35:01 B484 MSG 422779  Command:  RCPT TO:<user@domain.com>
19:35:01 B484 MSG 422779  Response: 554 5.7.1 <user@domain.com>: Relay access denied

1. Properties of GWIA | SMTP/MIME Settings | Relay Host for outbound messages
2. Change the Relay Host by providing the Internal IP Address of the Host server rather than the DNS address.
   

Relay Host refuses the relay access because the DNS name of the server provided to the GWIA resolves the public address of the Host instead of the internal one. The Host is properly configured not to accept relay attempts publicly; however, it is defined for to relay for internal requests. The requests from the GWIA enters to the external address rather than the internal.