Email Open Rate
July 12, 2018
An Email Marketing Glossary Entry

What is an open rate?

In email marketing, the open rate is the ratio of the total HTML messages opened over the total delivered.

An opened email means that someone -- or something -- loaded the rendered HTML body of your message in their email client. For the sake of simplification, we can assume that opened also means that someone 'human' took at least a glance at the content. In the context of an email campaign, an opened email counts matters roughly the same as someone having seen your advertisement -- i.e., an impression, -- or glanced at your blog -- i.e., a visit. The open rate is the base engagement metric of any email marketing campaign.

On top of opens, most email marketing providers will also track the click rate. The click rate is the ratio of links followed by users from within the email body, over the total number of email messages sent. The click rate is typically much lower than the open rate. Messages need to be opened to be clicked: the number of users taking action on an email is, in most cases, a lot lower than that of those who merely read through it.

An opened email is the online equivalent of someone having seen your storefront in the physical world. In the same context, a click is the equivalent to someone walking in your shop after seeing an advertisement. To be clear, neither bought or did anything significant (yet) for your business at that point, but one is much closer to doing so than the other. Therefore the latter is a more valuable lead.

What Counts as an Opened Email?

For security reasons, and unlike their HTTP counterpart, email network protocols do not track "open." In other words, a basic email server does not know whether the recipient has opened the message or not. That's where email marketing service providers come in. Providers such as Drip, MailChimp, and Mailgun (to name only a few,) handle all the email transactions on behalf of their clients. These third parties provide custom SMTP back-ends services tailored and add a layer of functionality to the transactions.

Tracking opens -- and therefore allowing you to calculate open rates -- is one of these extra services that third-party email services provide. To track email opens, the provider adds a unique image tag to each mail it sends. When the recipient opens the email and requests the image, the document gets flagged as read, and the provider is then able to report that information back to the client. Unfortunately, this strategy is not very precise and does come with a few caveats.

  1. Email clients (such as Outlook and most web-based clients) that block images by default will not report opens unless the user has configured the client otherwise. For the same reason, any text-only email reading application -- or those where the images are explicitly turned off -- will not report the open. Such false-negatives can be misleading.
  2. Conversely, mobile email clients that include a quick preview feature -- a trimmed view of the incoming messages -- will report the email as opened, even if the user on the receiving end did not technically open the document. In other words, they may have simply peeked through the envelope. In that case, these are false positives. As with the false-negatives above, false-positives can lead to skewed statistics.

In short: when it comes to open rates, because of the technological limitations inherent to email delivery, you cannot assume on the report that your email provider sends back is going to be 100% accurate. However, because these two edge-cases often end up canceling each other, the numbers are usually good enough, statistically speaking, for email marketing purposes -- assuming, of course, a big enough sample.

How are Open Rates Calculated

When you send an email, there are several possible outcomes besides the message being read by the recipient. The email could be rejected by the server on the receiving end, based on some local firewall rule -- such as domain blacklists. The message could also reach the server but returned to sender because the email address does not exist on the network or else is unable to accept incoming messages.

In all cases -- rejected, refused or not found -- the message then counts as a bounce. In the context of an email campaign, the total number of messages sent minus the sum that bounced equals the total delivered.

The formula for calculating your email open rate is:

open rate = ( total opened emails / total delivered emails ) * 100
total emails delivered = emails sent - emails rejected

Let's use an example: Assuming you sent a batch of 1000 messages in an email campaign. 950 of those reached their destination, while 50 bounced for one reason or another. Of those 950, 200 get opened. Your open rate is 21%: ( 200 / 950 ) * 100.

Open Rate Calculator

Here's an interactive open rate calculator for your marketing metrics needs.

Email Campaign

Open Rate Calculator

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How Valuable is the Open Rate Metric?

You may be wondering why you should bother with open rates and what it means. For starters, keep this number in mind: 21. According to a recent (March 2018) study by industry leader Mailchimp, 21% is the average open rate for most email campaigns.

MailChimp sends billions of emails a month for millions of users. We track a lot of data. So we scanned hundreds of millions of emails delivered by our system (where campaign tracking was activated, and where users reported their industry) and calculated the average unique open rates, click rates, soft bounces, hard bounces, and abuse complaint rate by sector .1

That number varies among industries and target audiences, but it nonetheless hovers over that number. This means that if your open campaign rates are regularly lower than 21%, then it would indicate that either

  1. your list is not targeted correctly, or
  2. one of the following needs work:  your content, your message copy, your offer, your reputation, or maybe even your overall business model.

Your open rate could also be higher. In that case, you may want to start adding more subscribers or target a wider range of customers.

Save Some Money!

A low open rate can save you money. The truth is that keeping a subscribers list alive is costly. The bigger the list, the pricier it is to maintain. On the one hand, email marketing services do charge you based on the number of subscribers you keep. Hoarding subscribers for the sake of maintaining numbers high on an Excel column won't help your business.

On the other hand, you need to maintain this list regularly, keep it clean and account for its weight with every new campaign. That, too, is costly -- probably more than you think.

If you find that your list is inefficient, you could save a significant amount of time and money by pruning those subscribers who never open your messages. Be aware of the quirks of tracking opens: users may be reported as inactive only because they do not load your images.

Regradless, if someone has been on your list for over a year and never bothered opening your beautifully crafted emails, then it probably means that they're not interested in your product or service. Sending these subscribers more emails won't change their mind, considering that they never open them in the first place. Trimming your list of inactive subscribers will lower your total subscribers, but it will also raise your open rate. In the end, you'll look even better and will buy back some much needed time in the process.

  1. Average Open Rate for Email & Other Email Benchmarks - MailChimp, Email Marketing Benchmarks,
The Mailman

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