- Per Klaviyo, new email lists start on double opt-in unless you change your account's default. Check your main list today.
- I always use single opt-in for email. If someone typed in their email, they clearly want to be on the list. They shouldn't have to confirm twice.
- With double opt-in, anyone who doesn't confirm never enters the list or the welcome series. Across 4 consumable brands, welcome email #1 earns about 30x what emails #2 to #5 earn.
- For SMS, I use double opt-in. Klaviyo says carriers often require it, and it's required for abandoned cart texts in the US and Canada.
This is for Shopify founders who just found the setting, or who are wondering why their list is growing slower than their form submissions say it should.
What's the difference between single and double opt-in in Klaviyo?
Here's how Klaviyo describes the two:
- Double opt-in: a new subscriber must confirm their subscription before they're added to the list. Per Klaviyo, people who don't confirm aren't added to the list or queued for a welcome series.
- Single opt-in: people are added to the list as soon as they sign up.
One detail most founders don't know: per Klaviyo's help center, new email lists inherit your account's default opt-in setting, "which is double opt-in unless you change it." New SMS lists start with double opt-in too. And changing the account default doesn't update lists you already have, so you have to check each list on its own.
Is Klaviyo double opt-in on by default?
For email lists, yes, unless someone changed your account's default. That's why I check it in every account I take over. It doesn't really matter where an account starts. What matters is that you look at the setting and make it what you actually want.
Why I use single opt-in for email
Think about who's filling out your signup form. A lot of them are non-customers coming in from a cold ad for the first time. They've never bought from you. They saw an ad, clicked, liked what they saw enough to type in their email, and now they're heading into your welcome series.
That's exactly the moment I don't want to add layers. Every extra step between "I'm interested" and "here's your offer" is a place where someone drops off before they place an order.
And that's what double opt-in adds. It's a second step: sign up, then go to your inbox, find the confirmation email, and click it. In reality, a lot of people don't complete both steps, and they end up missing out on your emails entirely.
My view is simple. When I set up email capture, I want new signups added to the list automatically. If someone entered their email, they clearly want to be on the list. They shouldn't have to confirm twice.
What happens to your welcome series with double opt-in?
It starts only once someone confirms. Klaviyo says people who don't confirm aren't added to the list or queued for a welcome series, so a list-triggered welcome flow never fires for them.
That matters because of where the money is. Across 4 consumable brands I work with, welcome email #1 earns about $4.50 per person. Emails #2 to #5 earn about $0.10 each. That's about 30x. The first email someone gets from you is the one they're most likely to act on.
With single opt-in, that first email goes out right away, while the person is still on your site thinking about you. With double opt-in, it waits on a click in their inbox, and for everyone who never clicks, it never goes out at all. I walk through how I build that series in the welcome email series.
Doesn't single opt-in let junk addresses in?
Some, yes. Typos and fake addresses can get on the list without a confirmation step. I'd rather handle that with how you send than by making real buyers jump through a hoop.
Two things take care of most of it:
- Send campaigns to engaged segments, not the whole list. At a fitness tech brand, an engaged send to 7,145 people earned $0.19 per person, while a full-list blast to 49,475 people earned $0.04. Who gets the email matters far more than how they got on the list. My approach is in email segmentation for ecommerce.
- Run a sunset flow. People who never engage get a last chance, then get suppressed. That keeps dead addresses from dragging on your sending and from padding your profile count. Here's how I build a Klaviyo sunset flow, and if your bill has crept up, why your Klaviyo bill went up shows where it usually comes from.
If junk is pouring in from one source, fix the source. My list growth playbook is in how to grow your email list.
Should you use double opt-in for SMS?
Yes. This is where I land on the other side.
SMS is a more acute form of marketing. You aren't going to do much brand awareness over text. The messages are more timely and more urgent, so having people actively commit to being on that list really matters.
Klaviyo is direct about it too. Its help center says "you should always use double opt-in for SMS lists," that carriers often require it, and that single opt-in isn't recommended for SMS because double opt-in is required for abandoned cart texts in the US and Canada.
Two more details from Klaviyo's page:
- Transactional SMS consent, like order updates, is added to the profile right away. Double opt-in doesn't apply to it.
- For promotional texts, you can't send anything until the person confirms through double opt-in.
If you're still deciding whether SMS is worth adding at all, I cover that in should I add SMS marketing.
How do you switch a Klaviyo list to single opt-in?
Per Klaviyo's help center:
- Go to Audience > Lists & segments and open the list.
- Open Settings > Consent.
- Under Opt-in process, choose Single opt-in.
- Click Save.
A few things from the same page worth knowing before you change it:
- Imports: list imports don't trigger double opt-in.
- API sign-ups: if a list is named, that list's setting decides. If no list is named, the account default decides.
- Third-party forms: if your form tool already sends its own confirmation, Klaviyo suggests turning off double opt-in on the Klaviyo list so people don't get two.
What should you check first?
Open your main email list and check whether it's set to single or double opt-in. If it's double, turn it off and switch it to single opt-in. Then check any other list that feeds a welcome flow, since each list has its own setting.
Leave your SMS lists on double opt-in.
Unless your brand has a very specific reason to make email subscribers confirm, that one change is the whole fix.
Where these numbers come from
The welcome email numbers come from 4 consumable brands I work with: 2,897 campaigns and $17.7M in email revenue. It's a small sample, so treat it as directional. The $0.19 vs $0.04 comparison is from a single fitness tech brand. For how brands compare more broadly, see my CPG email marketing benchmarks.
FAQ
Does Klaviyo use double opt-in by default?
For email lists, yes. Klaviyo says new email lists inherit your account's default opt-in setting, which is double opt-in unless you change it. New SMS lists also start on double opt-in.
Does changing the account default change my existing lists?
No. Per Klaviyo, changing the account default doesn't update existing lists. Check each list under Settings, then Consent.
What happens if someone never confirms?
They aren't added to the list, and they aren't queued for your welcome series. Klaviyo also notes a profile can exist before someone confirms, but having a profile doesn't mean they joined the list or gave consent.
Does double opt-in apply to people I import?
No. Klaviyo says list imports don't trigger double opt-in. Only import people who actually agreed to hear from you.
Should I use double opt-in for SMS?
Yes. I do, and Klaviyo recommends it for all SMS lists. It says carriers often require it, especially for abandoned cart texts.
Founder of Bardown Digital, a Chicago-based Klaviyo email and retention agency for Shopify brands. He's worked with brands doing $500K to $100M a year, with $100M+ in email-attributed revenue across them.