Open rate is the percentage of delivered emails recorded as opened by their recipients. If 2,000 messages were delivered and 600 registered an open, the open rate is 30%. It was once the headline email figure; today it is a rough and often inflated signal that needs careful reading.
How open rate works
An open is recorded through a tracking pixel: a tiny, invisible image with a unique address placed in the HTML of the email. When the recipient’s mail app downloads images, it requests that file from your email platform’s servers, and the platform logs an open against that contact.
The method has three weaknesses. First, if images are blocked or the email is read as plain text, no open is recorded even though someone read it. Second, Apple Mail Privacy Protection, introduced in 2021, fetches images through Apple’s servers for users who switch it on, whether or not they read the message, so many of those contacts appear to open everything. Third, security filters at some companies fetch images and test links to scan them, which creates false opens and clicks on business lists.
Platforms also calculate the rate differently. Some count unique opens (each person once), some count total opens, and some now separate machine or privacy-generated opens. Before comparing figures, check which version you are looking at.
Why it matters
Open rate is still useful for comparing your own emails over time, especially subject line tests sent to the same audience, and a sudden fall across every mailbox provider can be an early warning that mail is landing in spam. It is a poor basis for decisions on its own because machines inflate it and image blocking deflates it. Clicks, replies, purchases and the click-to-open rate say far more about whether an email did its job.
There is a UK privacy question as well. A tracking pixel reads information from the recipient’s device, which is the kind of activity PECR regulates. The ICO’s guidance on storage and access technologies treats email tracking pixels as within scope, so consider whether you need consent to track opens, and explain the tracking clearly in your privacy information. The Data (Use and Access) Act 2025 is changing parts of PECR, so check the ICO’s current guidance rather than older articles. If you are unsure how the rules apply to your business, get advice specific to your situation.
Common mistakes
- Celebrating a jump in open rate that is really Apple Mail Privacy Protection, not more interested readers.
- Comparing your figure with an industry average calculated by another platform using a different definition.
- Picking the winner of a subject line test on opens when the other version produced more clicks or sales.
- Defining inactive subscribers by opens alone.
- Tracking opens without mentioning it anywhere in your sign-up wording or privacy notice.
How to act on it
Keep watching open rate, but as a trend line for deliverability and subject lines rather than a measure of success. If your platform can show privacy-generated opens separately or exclude them, use that view. Build your main reporting around clicks, conversions and revenue per recipient, with opens as a supporting figure.
Review how you describe open and click tracking in your sign-up wording and privacy notice, and decide with your adviser whether consent is needed. If open rate drops sharply across Gmail, Outlook and Yahoo at once, check your authentication and spam complaint data before rewriting subject lines, because the cause is often technical. Setting up email reporting that leads to decisions is part of my digital marketing strategy and consulting work.