If you got a login token email, that means someone (hopefully you!) is trying to buy a Leanpub book using your email address. This means you already have a Leanpub account for this email address, and you need to sign in to your account before you can complete your purchase. (Since Leanpub books are often published in-progress, we create a Leanpub account for you when you buy your first book so you can easily download updates to the book. Using the login token, we can add this purchase to your existing account, so you have one place to go for all your book downloads.)
If you are not trying to purchase a Leanpub book, don't worry! You can ignore the login token email. Your account is safe, and you haven't made any additional purchases.