Understanding Deliverability Best Practices

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There are a few best practice steps you can take when getting started with Klaviyo that help you get set up for future success. This article covers the basics of updating your email sending infrastructure, importing clean lists, and sending to engaged customers. We also cover some strategies for maintaining clean lists, providing your customers with the right email preference options, and sending great content.

Import Clean Lists

If you intend to sync over existing email lists or manually import existing lists into Klaviyo, your deliverability may be at risk if you don't clean them first. Your former email service provider (ESP) most likely provides a way to analyze the engagement level of your main list using data points such as open rates, bounce rates, and more.

Before you migrate any existing lists into Klaviyo, we recommend using all data available to isolate and remove any invalid or inactive emails that will only bloat your sending and drag down your deliverability. It's imperative that this is done in advance of your first send with Klaviyo.

Send to Opted-in Customers Only

Ensure that your main newsletter list only contains individuals who have opted-in and that you aren’t deliberately (or inadvertently) looping in those who never subscribed. We highly recommend that you keep customers and opted-in subscribers separate. A customer can become a newsletter subscriber at any time, and a newsletter subscriber can become a customer at any time. However, while customers may have placed an order, this does not necessitate opting in to receive regular email communication. If you send regular campaigns to everyone in your account regardless of whether they signed up for marketing emails, you will see increased unsubscribe rates and decreased engagement — both negatively impact your deliverability.

It is best practice to have new subscribers confirm their email addresses when they first opt-in. This double opt-in process helps you grow your list while minimizing abuse and preventing the accumulation of invalid or mistyped emails. If you have a paid Klaviyo account and have disabled double opt-in for one or more lists, you will need to be diligent about removing soft bounces from your account every month or so.

Learn more about the double opt-in process.

Manage Email Preferences

Add fields to your newsletter signup form and subscribe/manage preference pages so subscribers can choose how often they would like to receive emails from you. You can then segment based on these preferences and ensure your email sending takes into consideration the frequency preferences of your recipients.

According to eMarketer, 39% of email marketers that practice list segmentation see better open rates, 28% see lower opt-out and unsubscribe rates, and 24% see better email deliverability, increased sales leads, and greater revenue.

Make it Easy to Unsubscribe

If you don't allow recipients to opt-out and decide if and when they want to stop receiving your emails, they are more likely to mark your email as spam. Spam complaints are serious and can significantly damage your email deliverability.

If your abuse rate hits even 0.01%, inbox providers (e.g., Gmail, Hotmail, Yahoo) will start to consider you a "bad sender" and take matters into their own hands. They may flag your emails as spam for all recipients. As a result, it is best practice to place an unsubscribe link near the top of your email, as well as the bottom, to ensure recipients know the best way to signal they'd like to opt-out. A spam complaint is much graver than an unsubscribe.

You can also give subscribers the option to choose how often they'd like to receive emails from you. You can then segment based on these preferences and ensure your email sending takes into consideration the frequency preferences of those on the receiving end. As mentioned above, according to eMarketer, 39% of email marketers that practice segmentation see better open rates, 28% see lower opt-out and unsubscribe rates, and 24% see better email deliverability, increased sales leads, and greater revenue.

Create Engaging Content

Inbox providers use spam filters to determine whether or not your emails reach the inbox. While it’s possible to observe trends in spam filter behavior, spam filters are designed so that evading them can’t be perfected.

Here are a few ways you can be smart about your email content:

  • Avoid Spammy Subject Lines
    A lot of words can potentially trigger spam filters; thus, we’ve compiled some do’s and don'ts regarding subject line word choice. In general, avoid using all capital letters. Studies show that 85% of recipients prefer an all-lowercase subject line to one in all caps. Both all caps and excessive exclamation points can trigger spam filters. Avoid things like:
    • Using a lot of symbols!!!!!********
    • Including just one large image in your email
    • Implementing eye-catching or spam triggering phrases like "JUST THIS ONCE FOR A LIMITED TIME ONLY", "100% FREE!", "ACT NOW!"
  • Find a Balance Between Images and Text
    Emails that consist solely of images (or are super image-heavy) trigger spam filters. Instead, emails should contain a combination of images and text. Spammers often use images to avoid spam trigger words, but ISPs have evolved faster. Email on Acid found that emails should contain at least 500 text characters to dodge spam filters. If this is an issue for you, consider including contact information, legal disclaimers, an unsubscribe link, or a company address in fine print at the bottom of your email. Also, include ALT text for your images so subscribers can read a description if your images don’t load properly. ALT text is also crucial to ensure that your emails are accessible.
  • Limit the Number of URL Links
    Large amounts of hyperlinked text can be considered a red flag for inbox providers. Spammers typically include as many links as possible, both hidden and overt. While including a few well-placed links probably won't cause any problems, consider only including necessary links and avoid over-use, especially if you link to sites other than your own.
  • Avoid Unnecessary Code in Your Templates
    If you use our drag-and-drop template editor, we take care of this for you. If you're coding your own HTML templates or editing the source code of text blocks within our template editor, consider that extra tags and poor code can trigger spam filters.
  • Get Personal
    The more personalized your emails are, the more likely email clients are to deem them important. If an email client determines that you likely know the person you're sending to, this significantly lowers the risk of your email ending up in spam. Klaviyo makes it easy to insert a recipient's first name into the subject line and body of an email. You can also ask your contacts to add you to their address books, or try using plain text emails as opposed to formatted ones. When in doubt, run your email templates through free spam filter tools online, like Mail Tester. This can help flag issues with your content that may be causing email clients to flag your emails.
  • Add Two Unsubscribe Buttons
    Consider adding one to the top of your email and one to the bottom. Letting people opt out when they no longer what to receive emails will reduce spam complaints and increase open rates over time as you begin to send to a more engaged list overall. While you don't want high unsubscribe rates, you'd much rather someone unsubscribe than mark your email as spam.

Explore our guide to learn ways you can be smart about your email content.

Create an Engaged Segment

Not only should you send to opted-in contacts only, you should also aim to send to engaged subscribers; otherwise, you risk hurting your deliverability performance. Moreover, when migrating from another email service provider (ESP), building an engaged segment and warming your sending infrastructure is essential. To isolate engaged subscribers, create an engaged segment; then, target this segment when sending campaigns.

For more information on how to do so, head to How to Create an Engaged Segment.

With the release of iOS15, macOS Monterey, iPadOS 15, and WatchOS 8, Apple Mail Privacy Protection (MPP) changed the way that we receive open rate data on your emails by prefetching our tracking pixel. With this change, it’s important to understand that open rates will be inflated.

If your campaign analytics show a large number of iOS openers, we suggest identifying these affected opens in your individual subscriber segments.

For complete information on MPP opens, visit our iOS 15: How to Prepare for Apple’s Changes guide.

Conduct Regular List Cleaning

Don't give email clients an excuse to flag you. Use segments to analyze your subscriber base and determine who actually engages with your emails. Most major email clients (like Gmail and Yahoo) track how recipients interact with emails from your domain — how many emails are marked as spam, how many are opened, how many bounce, etc.

They use this information to determine where your emails will be placed, whether it’s in the recipient’s inbox or their spam folder. Having a list that contains uninterested people or a high percentage of invalid emails will only hurt your efforts to reach those who actually do want to receive your emails.

Explore our Guide to List Cleaning for more information.

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