Understanding email deliverability

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Learn more about deliverability and the steps you can take to establish a strong sending reputation to ensure that your emails are delivered to the inbox.

Email deliverability is defined as when an email successfully reaches the inbox. It is a nuanced concept, and there are several factors that influence an email’s likelihood of being successfully delivered.

What is email deliverability?

Email deliverability is when an email is successfully delivered to your recipient's inbox (including tabbed inboxes, such as Google’s Promotions tab). Placement of that email (i.e., in the inbox, spam folder, etc.) is dependent on the reputation of that email.. Spam, at its most basic definition, is unwanted emails.

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

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 your email
  4. Your sending infrastructure

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

Deliverability best practices

Warm your infrastructure 
There is an infrastructural element to your sender reputation. This can either be Klaviyo’s default infrastructure, or dedicated infrastructure. Both still require an element of warming. Learn more about the ways in which you should warm your account.

Send to engaged contacts

When recipients engage with your emails, inbox providers (e.g., Gmail, Yahoo, Web.de, etc.) notice and reward you with inbox placement. There are positive engagement metrics that you can measure, and many more that you don’t have access to, but the inbox provider does. Engagement that you can measure is open and click data.

However, inbox providers may look at how long someone views an email, if someone moves emails from the spam to inbox folder, and if they add you to their address book. Since inbox providers don’t have access to your ecommerce data, if someone has previously purchased from your store, they have no way of knowing this. That is why it’s so important to include open and click data when identifying engaged contacts.

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.

Klaviyo's segmentation tool makes this easy. You can hone in on engaged contacts using open and click data in Klaviyo if you’ve been using the platform for a while; if you’re a new customer, use historic open and click data from your previous ESP (email service provider). If you’re new to Klaviyo, head to our data migration guides to ensure that you properly leverage historic engagement data in segments and start off on the right foot. 

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


This segment also has a condition to include people who were recently added to your newsletter list. This ensures that new signups are automatically added to this segment before they have the opportunity to receive and open/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.

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 that your subscribers want to receive

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 because 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 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 third-party URL shorteners (e.g., Bit.ly).
  • Include product recommendations and personalization tags to customize the message to your recipients.
  • Offer your recipients the option to update their email frequency or content preferences. If you don't, recipients may simply unsubscribe instead.

For more information on how to craft great emails, check out our course on getting started with email design.

Review your sending infrastructure

There are several elements that make up your sending infrastructure; the most important are:

  • IP address
  • Sending domain
  • Click tracking

When you sign up with Klaviyo, you're automatically placed on a shared sending infrastructure. While this allows for a quick transition to Klaviyo, you should consider setting up a dedicated sending domain sooner rather than later. This will allow you to build that strong sender reputation early on and does not require any additional warming or ramp up of volume per campaign send.

If you decide to alter any of these factors beyond Klaviyo’s standard configuration, you'll 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

You should continually track and monitor your email performance metrics to ensure your deliverability and success as a sender. You can review your deliverability performance metrics against your industry and best practices in How to monitor deliverability performance guide.

  • Open rates
    You should aim to target or exceed the rates relative to your specific ecommerce industry.
  • Bounce rates
    Your bounce rates should aim to be as close to zero as possible and never increasing. If your bounce rates are above this, it’s time to clean your lists, exclude older mailing lists, and reviewing how you acquire subscribers in the first place.
  • Unsubscribe rates
    Your unsubscribe rates represent ​​the number of recipients who unsubscribed divided by the total number of recipients. In general, you should aim to be under 1% unsubscribe rates per email campaign. However, keep in mind that having or even encouraging unsubscribes rather than spam complaints, is more beneficial to your reputation.
  • 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 0.2%. If your spam complaint rates are above this, it’s time to clean your list, narrow your segment engagement criteria, review your sending infrastructure, 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.

It's important to adhere to sending best practices to ensure that you have great deliverability, and actively monitor your metrics via your reports. You may also want to employ third-party inbox monitoring tools to help test and shape your approach to remediating any deliverability issues.


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