Explanation:

Let’s look at your options for storing contact info, and which one actually fits:

- Address box – This isn’t really a thing for contacts. Usually, it's where you type in an email address when you’re composing a new message.

- Message box – That’s just where you write your email or type a message. It doesn’t store contact info.

- Address book – This is the spot. It’s literally built for saving and finding email addresses and contact info fast. Almost every email app has one.

- Message book – Not a real feature in email. No one uses this term.

So, here’s what it comes down to: if you want to save contacts and pull them up quickly, you use the Address book. That’s exactly what it’s for.