I have just installed Exchange 2007 (after many issues). 1 cas+hub role server , and 1 mailbox role server.
I am reading some guides to tun things up and read this:
“…Because your server (cas+hub roles) is sitting directly on the Internet, you may want to change the advertised FQDN that is sent in HELO/EHLO commands in SMTP. The UI for both send and receive connectors allows you to configure this…”