I'd say everyone should be using https, the secure variant of the web's http protocol, to read and send email. That gives you an encrypted connection between your machine and the mail server, preventing anyone in between from looking at your mail.
More-or-less everyone uses https for logins, to protect the passwords, but not all use it for the actual data transfers. Check your service. Being a paranoid, I'd say if they don't support https, you should change providers. (Old joke: "I know I'm paranoid, but I'm really worried about whether I'm paranoid enough.")
Gmail has offered https for years; that was the main reason I switched to it. Last year, they went further; it is now the default, so everyone there gets it unless they actually turn it off. As I see it, all web mail services should do that.
Hotmail were a few years behind in offering https, but they now do. You have to muck around in menus and check "always use https" to get it, though. I do not know what other services do.