The server at your ISP is rejecting the connection since it does not see the doaming address coming from mail server.
As long as the Outgoing Domain is set on the SMTP gateway, mail server will send it with the "HELO".
Since you say its set, it could be that your ISPs mail server sees it, but doesn't like it. Try using one of your other local domains instead of mail.hopestar-b-cohiper.com,
