I would add that if you are really concerned about email security you would not be using any Gmail, Hotmail or Yahoo unless you are using something like PGP. They all have has contextual advertising based on the content of your email, so they are being scanned for the purpose of displaying "relevant" ads. I use Gmail and Yahoo only for things like news alerts and subscriptions - I never use them for personal email.
Using email on BIS is no different than POP or web based email... no more or less secure. If you are using BIS on unsecured Wifi you might as well tell the world because it is easily intercepted.