I use Webmail quite often and haven't personally seen this problem previously, however I've just tried to load it and found I could re-create the problem.
For the moment, I'd suggest :-
1. Load webmail via https://webmail.optusnet.com.au (the https:// at the beginning is important)
2. Enter your username and password as normal
3. Make sure that the "secure" radio button is checked
4. Press the login button
When I has "insecure" checked then the Webmail login took forever, but when I selected "secure" it pretty much loaded immediately.