My gmail is through my grad school. To access it through the web, I need to log into the school's alumni network, then it does a pass-through to email/gmail. For some reason, that pass-through doesn't work on my Mac; I've tried with Firefox, Safari, and IE. It just opens a new window of the alumni network.
Very odd, because on any PC it works smoothly. Probably a quirk with the school's system. I'm sure I can't be the only person who has a Mac, but it just never seemed a high priority to complain (and I don't know who to complain to). I use the Mac Mail through POP/SMTP when I'm on my Mac, or just use my iPhone (same way, but oddly I can use web gmail on my iPhone with Safari).

And no, I can't log into gmail directly. The school has it rigged that you need to use their system. I get username/pw issues if I try.

I've said I was tempted to just get a whole separate gmail so I didn't have to deal with this, and I think I have one (probably more than one), but just never use it, and it probably went inactive. Most (95%) of my email goes to a virtual email address; I just need to say which email to actually send it to.