I have exchange 2003 with SP2 running on windows 2003 server and IIS6.
I get https://myemailserver/exchange
to work and it goes to the certificate warning page and then to the login page.
But when I goto https://mail.mydomain.com/exchange externally (outside the domain) it goes to a 404 page not found error.
Please note: http://mail.mydomain.com/exchange works just fine externally and http://myemailserver/exchange
work just fine internally without any issues.