I use email forward and haven't had problems with my steam account, not sure about hosted emails, though I suspect there shouldn't be an issue. Do you have SpamAssassin set up?
I'm not sure =\ the way it sounds, you should be able to get emails from Steam just fine. Are you able to get other emails just fine? If you'd like me to test I can send you an email or you can send one to the address using email from another domain (like gmail) just to make sure you're receiving emails at all.