How to Build Your Email List

Sign up - 3d render illustration of text on black chalkboard in a room.

Since Klaviyo is an email marketing software, we often discuss best practices for campaigns and flows to make sure you’re getting the most out of our features. However, as you well know, you need to have contacts to market to before you employ any of these best practices. The larger your list size, the higher the impact each of your emails will have. So, it’s easy to see why list growth is an absolutely essential component of maximizing your email marketing revenue. You’re probably wondering, then, how to build your mailing list.


Klaviyo offers three variations of list-building tools — embedded signups, popups, and fly-outs. They’re all customizable and incredibly easy to set up. We outline how to configure all three in our docs, but here’s a quick breakdown of what each entails:

Embedded Signup Form

Embedded Signup: An embedded signup is usually placed in the header or footer of your site, and often only has one field where potential subscribers can input their email addresses (as opposed to a field for first name, last name, etc.). Alternatively, you may choose to have an entire page on your site dedicated to collecting email addresses, in which case you would use an embedded signup with several fields. Most companies typically include a simple embedded signup in the header or footer of their site in addition to a popup or fly-out.



Popup: A popup is set to appear on a page after a designated amount of time, or when a website visitor scrolls to a certain area of the page. This is the most aggressive of the three options, since it blocks the entire page and requires visitors to take some action, whether it be subscribing or exiting the screen.



Fly-out: Similar to a popup, a fly-out will appear on a page after some specified amount of time, or when a site visitor scrolls to a specific point on a page. The key difference between the two is that a fly-out doesn’t take up the entire page, but usually appears from the side or in the lower corner of the screen. Because of this, it’s less obtrusive and oftentimes a happy medium between an embedded signup and a popup.

With Klaviyo, you can customize the text, timing, colors, font, and button layout of your list-building tools. You can also add additional fields to collect more information (in case you’d like to create segments based on these data fields), but bear in mind that the more effort required to sign up, the less likely people are to do so. If you’d like to customize these even further by adding images, for example, we integrate with a number of great products that specialize in email collection. Here are two integrations we highly recommend:

Both Justuno and SumoMe offer advanced customization options. Justuno allows users to add personalized messages to their promotions, and has special recovery features for abandoned cart pages.

Double vs. Single Opt-In

Which opt-in method is most effective is subject to much debate in the marketing world. Some experts argue in favor of double opt-in because it usually leads to a more engaged list, while others advocate for single opt-in because it drives sheer numbers.

Single opt-in, because it is the path of least resistance, does indeed lead to more signups. However, since the the email addresses aren’t verified, it can also lead to bounces (if an address is incorrectly inputted) or more emails being flagged as spam (if subscribers weren’t sure they actually wanted to subscribe). Many studies have been conducted to determine which option is better, and data shows that double opt-in leads to 40% higher email open rates (source).


Building your email list is the first step of organizing an effective email marketing strategy. Whether you choose double or single opt-in, you should make sure you have an embedded signup form in the header or footer of your homepage, as well as a popup or fly-out to collect addresses. You should also include signup areas on your blog and other relevant pages to cast the widest net possible.

Do you prefer popups or fly-outs? Double or single opt-in? Let us know in the comments.


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How ISPs Think to Determine Email Deliverability



Daily Sending — Yea or Nay?


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  • I had to learn some of this the hard way while working on our email campaign for our startup here at I do have to say that double opt-in had worked better for us.

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