Well, https and port 80 will definitely not work together. If anything it would be port 443, which is the default.
With https, there are a lot more possibilities for failure - e.g. intranet.yourdomain.com might be signed by a certificate authority that is trusted in your own network's browsers, but not by Java (which is what sync is running on). If you inspect the certificate that this site presents to you, can you check who issued the certificate? The thread you link points to trust issues - and https is about encryption as much as it is about trust that the server you're talking to is indeed the server that it claims to be. There'd be no use in setting up encrypted communication with a random attacker, imposing as your own server, thus the trust relationship requirement.
So: In your browser, inspect the certificate you get from the host and let us know if it's issued internally, e.g. by your own company, or by a public certification authority - there are a few hundred that are typically installed as trustworthy in your browsers (sic), common examples would be GoDaddy, Verisign, Digicert (just what comes to my mind, this implies no recommendation for any of them)
