The best way to work with email on anyone else's computer is to use webmail, Browse to your email provider's website in your browser and look for an option to access email. You could install a mail client on the portable computer, but what you see will depend on what type of connection the account uses. If it's POP, you will see only newly arrived messages, and you'll need to be wary of leaving the only copy of messages you read on that computer. If it uses IMAP, you'll be able to see pretty much all of your saved correspondence. You'll still need to think about clearing messages from the computer when you return it, and probably you'll also want to remove Thunderbird (and its profile) to remove access to your email account when the computer goes back to its owner. However, Webmail will leave nothing behind on the borrowed computer, so is the most private method.