A double opt-in is anytime an email is sent to a customer to confirm their desire to subscribe to a list.
The problem that double opt-in is designed to solve is that we have no way of knowing whether the email address they entered in the signup form actually belongs to the person who entered it. Anyone who knows your email address could put that into any signup form out there. That sucks.
So without double opt-in, we have no certainty that it was actually that person who wanted to get emails, and that can be a problem if that person decides to go after you for spamming. Having the electronic paper trail of a double opt-in keeps you safe.
It's true that some people are not going to confirm. They forget. They change their minds. They get busy. The email doesn't reach them. Whatever the situation, you will lose a small percentage of subscribers.
It is also true that the subscribers you do get will be more committed. They've actively confirmed, which means you know everyone on there really does want your emails. That's a good feeling to have.
There's also a psychological trigger known as Commitment and Consistency that'll start playing in your favor. What it says is basically that we have a tendency to stay congruent with our earlier choices, no matter how small. So the simple act of confirming their wish to receive your emails is going to make them more likely to want to continue to receive and read your emails, and possibly even buy from you later.
In short, it's always a good idea to require double opt-in.
Also know that if the person has already confirmed their subscription for one list, we don't require them to confirm again when subscribing to another list. Once per business should be enough.
The only times I wouldn't do a double-opt-in is if I'm making a quick throw-away list for, like a party invitation or something, where it's really no big deal.
The next piece is to make sure you write a compelling confirmation email.
In the email, remind them why they signed up. Remind them of the benefit to them: The free gift they receive, or the awesome insider tips, or whatever it is.
You really need to make sure that you seal the deal in that email.
Use the text on the button wisely. Maybe they want to click that button.
That's it! You're in the clear, legally. People get their stuff and they're going to love you more and buy more from you.
What's not to like about that?
When you're using double opt-in ("requires confirmation") on your list, it will mean that some of the people who subscribe may not confirm their subscription.
A typical unconfirmed rate is between 5% and 20% of signups.
There are many possible explanations for why people don't confirm their subscriptions: