Learn the difference between single and double opt-in, why double opt-in is important, and how to set a list in Klaviyo to single opt-in.
Lists are set to double opt-in by default in all Klaviyo accounts. We strongly caution against using single opt-in on any of your lists unless you have a specific use case that calls for it.
What Is Double Opt-In?
Double opt-in is a process through which a new subscriber must confirm their subscription before being subscribed to a given list. It is the same for both email and SMS subscribers.
When a Klaviyo list has double opt-in enabled, new subscribers will receive a confirmation message immediately after signing up. This message will prompt them to confirm their subscription. Only subscribers who confirm their subscription will be successfully added to the list. Learn how to review and edit opt-in related pages for a list.
If someone provides both their email and SMS, confirming their consent by text will opt them into SMS and email. If they do so by email, they will only be opted into email.
Double opt-in is set at the list level. If a list has double opt-in, everyone who subscribes to that list must confirm their interest before they're added. The only exception is for SMS subscribers in the UK and Australia. Since alphanumeric sending IDs cannot receive text messages, there's no way for a subscriber to confirm that they want to opt in. Thus, even if a list is set to double opt-in, UK and Australian SMS subscribers will always go through single opt-in.
New subscribers will not get queued up for a welcome series until they have confirmed their subscription via the double opt-in process.
Why Is Double Opt-In Important?
When you add a signup form to your site, you are not able to control who decides to take advantage of this form. Even if you add an extra level of validation, it isn’t always possible to ensure subscribers only submit valid or accurate email addresses and phone numbers. Well-intentioned subscribers could simply type their email or phone number incorrectly, but spam-bots could also find your form and flood it with fake email addresses or phone numbers.
The double opt-in process helps you grow your list while also minimizing abuse and preventing the accumulation of invalid or mistyped emails and phone numbers. For email in particular, this is important because most major email clients (like Google and Yahoo) track how recipients interact with emails from your domain — how many are marked as spam, how many are opened, how many bounce, etc.
They use this information to determine whether your emails are classified as spam. Having a lot of uninterested people or a lot of invalid emails on your list will only hurt your efforts to reach those that actually want to receive your emails.
Enable Single Opt-In
In some specific cases, you may want to remove double opt-in and make your list single opt-in. Most often, customers choose to implement single opt-in when they are using other third-party signup forms or tools and their customers are prompted with a double opt-in confirmation at some other point in the signup workflow. For example, if your third-party signup form has a double-opt in feature enabled, you might want to disable double opt-in on your Klaviyo list so customers don't experience multiple opt-in confirmation messages.
Single opt-in is not recommended for SMS, as some carriers require you to have double opt-in enabled.
To enable single opt-in for a given list:
- Click into the list you want to edit
- Select Settings
- Check the box next to Single opt-in
- Click Update List Settings
Once this setting changes, when someone subscribes — to email, SMS, or both — they will not need to confirm their subscription. For instance, if someone subscribes via a form and the list they're sent to is single opt-in, they will be added to that list immediately.
What Happens if Someone Does Not Confirm Subscription
If someone subscribes to a list via a Klaviyo signup form on your ecommerce site and the list is set to double opt-in, but fails to confirm this in the double opt-in message, Klaviyo creates a blank profile for this individual. That means that this contact is not added to a list and has no further information or activity listed on their profile other than the form’s general properties (such as first name, last name, email address, and phone number).
However, if you use a third-party form, or the signup is passed through our API, Klaviyo will not create an empty profile— instead the subscriber will only sync into your account if they’ve confirmed opt-in.
At this stage, the contact becomes cookied, meaning their future interactions with your brand will be tracked as events on their profile. This means that they can be added to behavior-based segments, even though they are not subscribed to any particular list. It's important to note that these profiles cannot be identified with UTM tracking as Klaviyo does not track who confirms the double opt-in message.