Introduction to Email Deliverability

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Email deliverability is defined as when an email successfully reaches the inbox (including tabbed inboxes, such as Google’s Promotions tab). An email is unsuccessfully delivered when it ends up in the spam folder or is blocked from reaching the inbox entirely. Spam, at its most basic definition, is unwanted emails.

New to deliverability? Check out our deliverability glossary to familiarize yourself with key terminology.

Email deliverability is a nuanced concept, and there are several factors that influence an email’s likelihood of being successfully delivered. The four key points that influence email deliverability, and the reputation of you as a sender, are:

  1. Your initial sending habits when starting with Klaviyo
  2. Who the email is sent to
  3. The content of the email
  4. The sending infrastructure

Often, email deliverability issues can be solved by adjusting the group of people you send to. If you send relevant content to an engaged group of contacts, then monitor the performance of these emails, you can positively influence your sender reputation, and thus your deliverability.

There is also an infrastructural element to your sender reputation. In most cases, this something that Klaviyo automatically establishes for you when you sign up; however, if you have a dedicated sending domain and/or dedicated IP address, there are some additional steps you’ll need to take to ensure that you start off on the right foot. Not all Klaviyo customers are eligible for (or should have) dedicated sending infrastructure, and changing these elements won’t solve your deliverability woes if you don't also practice good sending habits. See below for more information on who should have a dedicated domain and/or IP.

In this article, you will learn the steps you can take to establish a strong sending reputation and ensure your emails are delivered to the inbox.

Warm Your Sending Infrastructure

If you’re just starting out with Klaviyo, it’s critical to warm your sending infrastructure, regardless of whether you’re on shared or dedicated. This trains inbox providers to recognize you as a “good” sender and kicks off the process of building a positive sender reputation.

Warming your sending infrastructure involves turning on high engagement flows (e.g. welcome series and abandoned cart) and sending to engaged contacts, as outlined below, on a set schedule. This schedule and the exact segments you send to will vary depending on how many contacts you have in your account and what your open rates are. To learn what warming schedule is right for you, check out our guide to your first send.

Send to Engaged Contacts

When recipients engage with your emails, inbox providers (such as Google, Yahoo, etc.) notice and reward you. Engagement is defined as strictly email engagement, e.g. opening or clicking your emails. Inbox providers don’t have access to your ecommerce data, so if someone has purchased previously, they don’t have any way of knowing this. This is why it’s so important to include open/click data when identifying your engaged contacts.

Klaviyo makes it easy to isolate a group of engaged contacts using segmentation. You can hone in on engaged contacts using open/click data from Klaviyo if you’ve been using the platform for a while, or, if you’re a new customer, you can use historic open/click data from your previous ESP (email service provider).

If you’re new to Klaviyo, be sure to check out our data migration guides to ensure that you properly leverage historic engagement data in segments and start off on the right foot using Klaviyo.

Below is an example of a 30-day engaged segment that leverages Klaviyo engagement data as well as engagement data from a previous ESP (in this case, Sailthru).


Notice that this segment also has a condition to include people who were recently added to our newsletter list. This is important because it ensures that new signups are automatically added to this segment before they have the opportunity to receive and open or click an email. Brand new subscribers are likely to be highly engaged since they recently expressed interest in your brand.

However, if you’re using the segment above as a guide and you imported your newsletter list fewer than 15 days ago, delete this condition so that only new, organic subscribers are included. Otherwise, everyone on your newsletter list will be included, regardless of when they were collected in your prior ESP.

Send Great Content

The content of your emails also has an impact on your sender reputation. Put yourself in your customers’ shoes when developing the content of your emails. Some high-level tips to keep in mind are:

  • Don’t use image-only emails. These can trigger spam filters as phishers often use image-only emails to deceive recipients. Be sure to include some text in your emails, including alt-text, even if only in the header and/or footer.
  • Don’t include numerous links to external domains. The majority of the links in your emails should lead back to your website. Links to external domains can trigger spam filters as this is also a technique that is often used by phishers.
  • Don’t use 3rd-party URL shorteners (e.g.,
    Include product recommendations and personalization tags to customize the message to your recipients.

For more information on how to craft great emails, check out our email design guide.

Review Your Sending Infrastructure

There are several elements that make up your sending infrastructure, most important of which are your:

  • IP address
  • Sending domain
  • Click tracking

When you sign up with Klaviyo, you are automatically placed on shared sending infrastructure. The vast majority of customers do not need to alter these settings. However, if you are sending a high volume of email or consistent branding is extremely important to your business, you may choose to alter any of the above.

When you do decide to alter any of these factors beyond Klaviyo’s standard configuration, you will need to make updates to your DNS records. This includes when you set up a dedicated sending domain or dedicated click tracking, or when you are given a dedicated IP address by Klaviyo. Not all customers are eligible for a dedicated IP address, and there are pros and cons associated with dedicated vs. shared IPs.

If you believe you qualify for dedicated sending infrastructure, please review our guide to Dedicated Sending Infrastructure.

Monitor and Adjust Your Sending

Your business, your customers, and the world of email are ever-changing. Monitor your sending to adjust to changes and stay at the top of your game. The key things to keep an eye on are:

  • Open rates
    Ideally, your open rates will be above 15%. If you notice your open rates dip below 10%, it’s time to take action.
  • Bounce rates
    Your bounce rates should be below 0.8%. If your bounce rates are above this, it’s time to clean your list.
  • Unsubscribe rates
    Your unsubscribe rates should be below 0.3%. If your unsubscribe rates are above this, narrow the engagement criteria on the segments you’re sending to.
  • Spam complaint rates
    The spam complaint rate is the ratio of people who actively mark your email as spam out of the number of people who received the email. This should be below 0.08%. If your spam complaint rates are above this, it’s time to clean your list, narrow your engagement criteria in the segments you’re sending to, and re-evaluate the content of the emails you’re sending.

The difficulty with deliverability is that you don’t always know when your emails have been successfully delivered. Inbox providers use a combination of different metrics to evaluate your emails and, to protect against spammers, these metrics and methods are purposely kept hidden from senders. Because of this, it's important to adhere to sending best practices to ensure that you have great deliverability.


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