What are the main email metrics?

Email has the enormous advantage, compared to other channels, of being perfectly traceable in every aspect. It is always possible to track how many users open messages, how many have clicked within them, which emails brought more conversions and so on.

The key metrics email marketers are interested in fall into two categories:

  1. On-mail KPIs: these refer to the user’s interaction with the message itself. These metrics are tracked directly by the email marketing platform, which makes them automatically available and easy to read. This category includes openings, clicks, unsubscriptions, bounces and so on.
  2. Off-mail KPIs: these measure everything that originates in the email to then go elsewhere, for example to an e-commerce site, website or blog. These metrics analyze various aspects relative to the email channel, such as the volume of traffic attracted, the average purchase amount, the conversion rate and so on. These are normally provided by analytics systems that are outside of the email platform, such as Google Analytics.

In this blog we will focus primarily on on-mail KPIs. So let’s delve further into the 10 basic metrics that every email marketer should know, follow and analyze.

1. Open Rate (OR)

Among email metrics, the open rate indicates the number of emails opened compared to the total amount delivered (or sent – fortunately these two values ​​overlap an average 99% of the time if sent by the MailUp platform!).

More technically, the openings are counted by the system through the inclusion of a transparent image that is recalled whenever the recipient displays the pictures in the message. A recipient can open the message multiple times, and consequently that email will have more “openings”. If the recipient does not download the images, openings cannot be detected.

The elements that affect opening rates most are the subject and preheader: carry out tests frequently and pay extreme attention when drafting interesting copy that arouses curiosity and urges recipients to open the message.

The formula to calculate it is: (Emails opened / Emails delivered) * 100

Also read: 9 Things keep in Mind for Writing Powerful Email Subject Lines

2. Click-through rate (CTR)

This is the number of clicks on the links contained in an email message, divided by the number of emails delivered. If a good open rate is indicative of a good subject, the click-through rate is determined by the email’s content – images, copy and especially calls-to-action.

To improve this crucial email KPI, it is important to carry out frequent A/B tests on wording and the style of CTAs as well as on the content layout and images used.

The formula to calculate it is: (Emails clicked / Emails delivered) * 100

3. Unique clicks and unique open rate (UOR)

Within your email metrics, make sure to differentiate the total number of openings or clicks – which also include multiple openings or clicks by the same user – from the amount of single users who have opened or clicked at least once. In this case, the terms unique openings or unique clicks are used.

Even if data obtained in this manner is cleaner and more precise than the total count, it’s not always worthwhile to distinguish this level. To understand the performance of a campaign, in fact, the more general values ​​of OR and CTR are normally more than adequate.

The formula to calculate them: (Unique clicks or unique openings / Emails delivered) * 100

4. Click-to-open rate (CTOR)

CTOR measures the number of clicks with respect to the number of openings, and is thus the most accurate metric for measuring the level of interaction that messages can trigger. How many recipients close the email immediately after opening it? And how many of them interact with its content and go to the website?

The formula to calculate it: (Unique clicks / Unique openings) * 100

5. Bounce rate

The bounce rate is the percentage of email addresses that returned an error after being sent. Errors can be either permanent(hard bounces) or transient (soft bounces). Hard bounces include non-existent or invalid email addresses that will never be delivered the message. Soft bounces, on the other hand, include full inboxes or temporary server issues – in these cases, delivery will ensue if the issue is resolved.

Monitoring bounce rates is above all crucial for ensuring that correct message delivery takes place. In fact, higher than average bounce rates may be a symptom of a problem related to a specific email client or to the message itself. Hard bounce rates are also one of the key elements used by internet service providers (ISPs) to determine sender reputation: this is why you should always clean up your lists in a timely manner when such issues arise.

The formula to calculate it: (Returned emails / Sent emails) * 100

6. Unsubscribe rate

Keeping track of subscription trends is important, but knowing how many users unsubscribe is equally important. A healthy unsubscribe rate should stay at low levels, less than 2%, and the number of unsubscribed users should always be lower than the number of new users.

If this value rises or hits peaks and valleys, it is time to ask yourself a few questions. Re-evaluate your sending frequency or your messages’ content and run several tests to identify – and correct – whatever may be the cause.

The formula to calculate it: (Unsubscribed users /Emails sent) * 100

7. Opens by device

Knowing if users open your messages on their desktop, smartphone or tablet is highly valuable information that allows you to design evolved and effective strategies. For example, knowing that the majority of users will read your messages from their smartphones provides specific indications regarding email design and the need to optimize it for an on-the-go display.

The MailUp platform provides this information both at the individual level and for an entire list. It also provides details relative to the type of device (Android, iPad, iPhone, Windows PC, etc.) and operating system (Apple OS, Apple MAC OS, Linux, MS Windows, etc.).

The formula to calculate it: Unnecessary, as the data is automatically calculated by the MailUp platform

8. Spam score

Anti-spam software like SpamAssassin assign scores to emails: they analyze an email in its entirety and give each item they perceive as a spam risk a number of points. If the sum of the scores exceeds a certain threshold (typically 5.0), the message has a good chance of winding up marked as spam.

This is why it’s always good practice to check the spam score of your messages and make sure it always falls well below the danger threshold. The MailUp platform automatically runs a spam check before each sending and highlights the main critical factors, allowing you to correct them before forwarding the message.


9. Conversion rate

Now that we have finished discussing the main on-mail KPIs, let’s analyze two – fundamental – off-mail KPIs that can be monitored by integrating email platform data with data from external analytical systems like Google Analytics.

Every email has (or should have) a clear objective that corresponds to the action you would like users to carry out. Some examples of objectives are: make a purchase, read an article on your blog, fill out a subscription form, request a quote or sign up for an event or webinar.

The conversion rate is the metric that measures how effective your message is in relation to your objective. It is important to be constantly aware of this metric on both a general level as well as by type of campaign or message, studying its history and averages at different levels. Conversions are intertwined with a call-to-action’s quality: this is why experimenting with and frequently testing CTAs is fundamental for guaranteeing their maximum effectiveness.

The formula to calculate it: (Number of users who have completed the action / Emails delivered) * 100

10. Return on investment (ROI)

Return on investment is clearly one of the key metrics to monitor because it accurately measures the cost-effectiveness of email campaigns, that is, how much they earn you in comparison with the costs incurred to implement them. This calculation is simple: take the total sales value or total revenue resulting from an email campaign, subtract the costs incurred to create it (including the platform, human resources and time put in) and divide the result by the same cost. Multiply by 100 to get your ROI.

We will never stop emphasizing that email is the channel with the absolute highest average ROI (400%) – an excellent reason to leverage this channel in the best possible way.

The formula to calculate it: [(Value of sales from an email campaign – Campaign costs) / Campaign costs] * 100


Data monitoring and analysis are fundamental in assessing an email campaign’s results. Setting clear goals and identifying the most relevant email metrics for your industry and activities is the way for getting the most out of every email campaign.


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