By Caleb Malik

Email marketing serves as a high ROI channel for organizations — if it’s done right. But how do you know if your email campaign is effective, and more importantly, valuable to your audience? You have two options: Interview customers, which is expensive and difficult. Or track these six important email metrics, which can tell you a lot about user engagement.

1. Open Rate

Unfortunately, there isn’t a universal benchmark for this KPI. That’s because open rates vary from industry to industry. Instead, think about open rate relative to previous sends.

For example, if 50% of subscribers open this month’s email compared to 30% of subscribers who opened it last month, the open rate metric tells us that people saw something in the subject line, or in the preview text, that caught their eye. Find out what that something is, and you can replicate a successful subject line for future emails.

Let’s say you’re sending weekly emails to subscribers and the click-to-open rate is twice as high for the email sent this week compared to last week. This metric is telling you that the email with the higher click-to-open rate included content in the body of the email that users found valuable.

2. Click-through Rate

This KPI gives you a big-picture idea of what your email list is doing for you. Let’s say you send 1,000 emails. Out of those 1,000, perhaps 50 people click through to your website, which is a 5% click-through rate. This indicates you have a healthy list and users find the emails valuable. But if out of 1,000 emails, only three people click through to the website, the metric reveals that your email list isn’t doing a whole lot. Even if users opened the email, they’re not ending up on your website.

3. Click-to-Open Rate

While the click-through rate gives insight into your email marketing in general, the click-to-open rate offers a glimpse into specific emails — or rather, how content performs from email to email. (The click-to-open rate is measured by dividing the number of unique clicks by the number of unique opens.)

4. List Growth Rate

If your list isn’t growing, it’s a problem. Most organizations see a loss of subscribers at about 20% a year, so to counteract that, you want to be adding people at a rate of at least double that number. This metric provides key intel into how your list is growing, and at what rate. Remember: At the end of the day, you only get as much out of your email list as its size.

5. Active Versus Inactive Subscribers

There’s a portion of your list that’s active. Of the last four emails, these are the people who’ve opened two or three. Then there’s the portion of your list that’s inactive. They haven’t opened an email in a month, six months, perhaps even a year. Before you can determine who’s active and who’s not, you should view this metric within the send frequency of your email campaign. An e-commerce company, for instance, might send two emails a day, and if a subscriber doesn’t open a single email for a full week, they would be labeled inactive. A DMO, however, might send one email a month, so it makes more sense to look at subscriber behavior over the last six months. Ideally, you’ll want to cull your list if the number of inactive users tops 10%. Culling the list not only helps maintain positive brand perception, it also makes sure your emails arrive in inboxes, not spam folders.

6. Conversion Rate

If subscribers aren’t using your email to do the things you want them to do — download a travel guide, buy a product, purchase tickets — then your business isn’t enjoying the ROI benefits of running an email campaign. That makes conversion rate the ultimate metric. It shows how many conversions each email drives. Be sure to mark email links with Urchin Tracking Module (UTM) parameters so you can track the traffic, and thus the conversions, coming from every email.