You might want to double check your company's network policy. It is quite possible that they block all mail aside from work mail for a (seems good to management) reason. Most likely, the firewall is set up to only allow email access to company servers. Where I work, after during the normal working hours, you can't access gmail/yahoo/hotmail, but they open them up after hours. There is also a policy stating that you're not to access web/free/personal/home emails during working hours while on the company network.
Safari displays websites because it's a completely different protocol. I bet if you tried to browse some known porn sites on your itouch, you'd get the same blocked message you will get on the company computer. That of course assumes that the company blocks them in the first place