Email acquisition is one of the most important parts of running an eCommerce business, and Klaviyo gives you several ways to collect subscribers. One of the most common questions new users ask is whether they should use single opt in or double opt in for their signup forms. Klaviyo supports both, but each one works differently and has different effects on list quality, deliverability, and overall growth.

Although Klaviyo’s default settings already promote healthy list building, every brand eventually faces the same question: is it better to let people join your list immediately after submitting their email, or should you require them to confirm their subscription before they receive marketing messages?

To help you decide, let’s break down exactly how single opt in and double opt in work inside Klaviyo, when to use each one, and how to change your settings at the list level.

Klaviyo makes everything in this guide possible, from segmentation to automated flows to advanced personalization. If you’re still using a basic email tool, switching to Klaviyo is one of the fastest ways to increase revenue without adding complexity.

You can test every feature, build your flows, and explore the platform with a free trial.

Start Your Klaviyo Free Trial Here

Single opt in is the most straightforward way to grow your email list. When a visitor enters their email into one of your forms and clicks submit, they are instantly added to your Klaviyo list and marked as subscribed. They can immediately receive campaigns, flows, and marketing messages because they are treated as an active subscriber the moment they sign up.

Single opt in is the most common choice for eCommerce brands because it removes friction from the signup process. Every additional step a visitor must complete increases the chance that they will abandon the process before finishing it. With single opt in, the person only needs to submit the form once and they are fully subscribed. This often results in faster list growth and higher overall subscriber volume, especially for brands running paid ads or generating steady organic traffic.

However, the simplicity of single opt in also comes with a significant drawback. Because the subscriber does not need to verify their email, you have no guarantee that the email address is valid. Bots, fake emails, spam traps, and mistyped addresses can all enter your list. Over time, this can inflate your subscriber count and hurt deliverability. Klaviyo will charge you based on the number of active profiles, so a high volume of low quality emails ends up raising your costs and weakening the performance of your account.

This does not mean single opt in is bad. It simply means that if you use it, you need to monitor new subscribers and have strong list cleaning practices in place. Many brands thrive on single opt in, but they do so because they regularly remove unengaged contacts and protect their deliverability through weekly or monthly list maintenance.

Double opt in adds an additional step to the signup process. After someone enters their email and submits a form, Klaviyo sends a confirmation email asking them to verify their subscription. The person must click the confirmation button or link before being added as a subscribed profile.

This extra step prevents low quality emails from being added to your list. Only people who confirm their subscription become active subscribers. Everyone who ignores the confirmation email remains unconfirmed inside your Klaviyo dashboard and is not billed as an active contact. This means double opt in naturally filters out fake emails, bots, and low intent subscribers.

Double opt in leads to a smaller subscriber list, but the contacts who remain tend to be more engaged. They had to take two actions, not one, which shows a higher level of intent. This usually results in better open rates, stronger click through rates, and improved deliverability.

There is, however, one issue to consider. Some legitimate subscribers never confirm their email. They may overlook the message, forget to click the link, or not recognize the confirmation email in their inbox. When this happens, the potential subscriber ends up in a kind of limbo inside your Klaviyo account. They are neither fully subscribed nor fully removed, and they will not receive any future communication from you. For brands with audiences that are easily distracted or not very tech savvy, this can result in lost subscribers.

The right choice depends on your goals as well as the quality of traffic coming to your site. For most eCommerce stores, single opt in is the better starting point because it allows you to grow your list quickly and ensures that subscribers can receive emails immediately. Reducing friction in the signup process often leads to more subscribers, more data, and more revenue opportunities if the list is maintained properly.

However, using single opt in responsibly means you must monitor the quality of your signups. If you ever see a sudden spike in new subscribers that looks suspicious, it is a sign that bots or fake emails may be entering through your forms. When this happens, switching temporarily to double opt in can protect your list. You should also have a consistent list cleaning automation active in Klaviyo to remove subscribers who never open your emails. This protects your sender reputation and keeps your Klaviyo costs aligned with your revenue potential.

If your store has a history of receiving low quality contacts or if you frequently get signups from regions known for bot activity, double opt in may be the safer long term option. Read our case study where we helped fix a client account that had this issue. It guarantees that every subscriber is real and that every address is valid. This is especially beneficial for brands that rely heavily on email deliverability or have had deliverability problems in the past.

In general, start with single opt in unless you have a clear reason to avoid it. Use double opt in if you encounter spam signups consistently or if you want to maximize list quality at the expense of slightly slower list growth.

Klaviyo manages opt in settings at the list level. Each list can be configured independently, which gives you full control over how different forms behave.

To adjust these settings, open the list that your forms are connected to. Navigate to the Settings tab for that list, where you will find the option to switch between single opt in and double opt in. If you select double opt in, Klaviyo will automatically trigger the confirmation email when someone signs up through any form connected to that list. If you choose single opt in, subscribers will be added immediately without additional steps.

If you use multiple lists for different purposes, make sure the opt in settings match your goals for each type of subscriber. Many brands keep their main marketing list set to single opt in while using double opt in for giveaway lists, influencer traffic, or regions prone to bot signups. The flexibility inside Klaviyo makes this easy to manage.

Both single opt in and double opt in are valid choices in Klaviyo. Each has strengths and limitations, and each can work well when managed correctly. What matters most is understanding the trade offs and choosing the option that protects your brand while supporting your email marketing goals.

Single opt in gives you faster list growth and fewer barriers. Double opt in gives you cleaner data and higher quality subscribers. Both can build strong email revenue when combined with proper monitoring, list hygiene, and consistent optimization.

If you maintain a healthy flow of new subscribers and clean your list regularly, single opt in is often the best choice for most eCommerce brands starting out. As your brand grows, you can adjust your approach based on performance, traffic quality, and deliverability needs.

Need help implementing this or other areas in your Klaviyo account? Click below to book a consultation call