Yeah, hotmail is the likeliest. Start putting in all your addresses in your hotmail address book and change your spam filtering to the 'exclusive' setting. I tried all sorts of things but found that was the only way to avoid loads and loads of crap about uni degrees and porn. Did a quick ask around and everyone who has hotmail has the same problem, regardless of their surfing habits.
I don't use my hotmail much because of this--only for instant messaging with the olds...
