What is Open Rate?

Open rate is the percentage of delivered emails that recipients opened. It is still a useful signal, but privacy features now make it less reliable.

For years, open rate was the first number every email marketer checked. If it went up, the campaign felt like a success. If it went down, people rewrote the subject line. That habit made sense once. Today, open rate is still useful, but it is not the clear truth it used to be.

In simple words, open rate is the share of delivered emails that were opened. The formula is: unique opens ÷ delivered emails × 100. Delivered means emails sent minus emails that bounced.

How the number is calculated

For example, suppose a coaching institute sends a newsletter to 10,000 students. 200 emails bounce, so 9,800 are delivered. If 1,960 people open it, the open rate is 1,960 ÷ 9,800 × 100 = 20 percent.

Behind the scenes, most email tools track opens with a tiny invisible image, much like a tracking pixel. When the email loads that image, the tool counts an open. This is why open tracking depends on images loading, and that is exactly where things changed.

Why open rate is less reliable than it used to be

In 2021, Apple introduced Mail Privacy Protection. When a user turns it on, Apple Mail can load email content, including that tracking image, in the background, whether or not the person actually reads the message. The result: many emails get counted as opened when nobody looked at them.

This inflates open rates, especially for lists with many iPhone and Mac users. Some other mail apps also load or block images in ways that blur the count. So a jump from 22 percent to 35 percent may not mean your subject lines suddenly got better.

How to use open rate wisely

Compare trends, not single sends. A steady drop over several weeks is still a useful warning sign.
Check whether your email tool can flag machine opens. Many platforms now try to separate them.
Pair it with clicks. Click-through rate needs a real action, so it is a stronger signal of interest.
Watch replies, conversions and unsubscribes. These show what people actually did.
Be careful with "inactive" rules. Inflated opens can hide who is truly inactive, and blocked images can make some engaged readers look inactive.

What a falling open rate can tell you

A sudden, sharp drop is often a delivery problem, not a content problem. If emails land in spam or a rarely checked tab, fewer people see them. This is why open rate is closely tied to email deliverability. Before rewriting your content, check whether your emails are reaching the inbox at all.

Subject line tests still have value too. If you run A/B testing on subject lines, judge the winner by clicks or sales where possible, not by opens alone.

Simple takeaway

Open rate is a direction signal, not a verdict. Use it to spot trends and delivery issues, then trust clicks, replies and sales to tell you whether an email actually worked.