Single Opt-In vs Double Opt-In

A Single Opt-In vs Double Opt-In strategy is one of the first decisions you will face when starting to build an email list. This begs the question: ‘what is the difference between double and single opt in?’

Many have suggested that it’s simply a question of quality vs quantity

  • If you want to grow your list as big as possible, as fast as possible, you choose Single Opt-In
  • If you are more concerned with building a qualified, engaged list, you choose Double Opt-In.

However, if it were that simple, wouldn’t every ecommerce merchant just choose Single Opt-In? After all, who doesn’t want to grow big and fast, right?

A better way to understand the two approaches is to use a fishing analogy…

Double optin is like fly fishing

Invest time and effort upfront into creating the right ‘bait’ to catch only your target species. Be prepared to test.

Source: The Paris Review

Single optin is like trawler fishing

Catch as much as you can. Then sort through it all to find the species you were after. Throw away what’s left.


Both are very valid approaches, with a similar outcome. But they will appeal to different people. So consider whether your store suits a trawling approach, or a fly fishing approach.

Let’s look how these two approaches apply to email marketing…

What is the difference between Single Opt-In and Double opt-In?

  • Single Opt-In is a one-step process. Enter your email address into a sign up form and submit. That. Is. It. No need to confirm your email address. You are immediately added to the email list.
  • Double Opt-In is a two-step process. Enter your email address into a sign up form and submit. Receive an automatic email requesting confirmation. Unless or until your email address is confirmed, you cannot be added to the email list.

There are a couple of reasons why many ecommerce merchants don’t like a Double Opt-In strategy.

Firstly, some will argue that it’s because they want to make it as easy as possible for people to sign up. But underlying this is usually the desire to simply grow as big and as fast as possible.

For others merchants, it’s because of the potential for complication with coupon codes.

Most ecommerce stores offer a coupon code as an incentive for shoppers to sign up. Typically, that code is delivered in a ‘Welcome’ email.

Therefore, the delivery of the coupon code is totally dependent on the Double Opt-In process:

  • Best case scenario: inevitably, it is going to slow down delivery of the coupon code
  • Worst case scenario: if the new subscriber doesn’t confirm their email, or if they do not meet the criteria for the Welcome flow, they will not receive the coupon code at all.

It’s the sheer simplicity of the Single Opt-In that appeals to many ecommerce merchants.

So it’s no wonder that ‘problems with double opt-in’ appears regularly in Facebook groups of Klaviyo users. And no wonder that search queries like ‘how to turn off double opt in klaviyo’ are so popular.

But just because you can turn off Double Opt-In, doesn’t mean you should.

Here’s the problem with Single Opt-In…

If you have no (Double Opt-In) confirmation process, two bad things are going to happen:

  1. You’re going to capture a lot of really crap data
  2. You’re going to acquire a lot of low-value, one-and-done customers.

1. Why does Single Opt-In capture crap data?

There are at least three good reasons why having no confirmation step is going to result in crap data:

  1. People make mistakes and sometimes accidentally mistype their email addresses (come on, we’ve all done it!)
  2. Some people will use fake email addresses just to grab a coupon code (just ask a bricks n mortar retailer how many fake emails get provided at POS)
  3. Spam, spam, wonderful spam! And there is a lot of it about.

According to Statista, 293.6 billion emails are sent every day in 2019. Unfortunately, more than half of it is spam.

Global email spam rate 2012 to 2018 (source Statista)

Kaspersky breaks it down my month…

Monthly email spam rates (source Kaspersky)

Without a confirmation step, all of that crap data (misspelt emails, fake emails and spam emails) is going straight into your newsletter list.

It will grow big and it will grow fast.

So why should you care about having crap data?

Assuming you have a Welcome email series in place, every time an email is added to your list (good or bad), it’s going to trigger an automatic email.

Every dud email address you send to is going to result in a ‘bounced email‘. This not only impacts the conversion rates of your sign up campaign, it will potentially damage your list reputation. Ultimately it will reduce the number of successful email deliveries in future.

2. Why does Single Opt-In acquire low-value customers?

Simple. Low barrier to entry.

Critics of the Double Opt-In process will say “the more effort required by a consumer to do something, the less likely they will do it“. That’s probably very true, for some consumers at least.

But stop and consider this type of consumer for a moment.

If these people cannot be bothered to…

  1. click to their inbox (or possibly spam folder)
  2. click a confirmation button

… ask yourself if they are showing the potential to be long-term, high-value customers.

If two clicks is too much effort, you seriously have to question how engaged they are with your brand. The harsh reality is they’re probably just not that into you.

Without the Double Opt-In process as a barrier to entry, many will take their coupon code, use it and you’ll never see them again. Wham, bham, thank you mam!

Double Opt-In will not eliminate this problem entirely. But it definitely helps to minimise the issue.

Having an email list full of crap data (ie. a high percentage of dud email addresses) will mean…

  • You are probably on the wrong Klaviyo pricing plan (ie. paying too much)
  • You will see lower open/click rates and higher bounce/unsubscribe rates
  • It will impact list reputation and future deliverability
  • It will actually take longer to grow a good quality list.


If your primary focus is simply to win a quick sale and you’re determined not to use Double Opt-In, try offering the coupon code without even asking for an email sign up.

If they go ahead and purchase, you will probably acquire their email anyway. And you’re less likely to end up with a glut of dud email addresses.

But if you really want to build a valuable email list of genuine prospects and customers, you must use Double Opt-In.

A Single Opt-In vs Double Opt-In strategy is not about quantity vs quality. It’s about engagement.

Don’t be tempted to cut corners. Remember: Avoid the trap of more haste, less speed.

Please leave a comment below and share your thoughts and experience.

Related Klaviyo help centre documents:

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