Open Rate

Open rate is the percentage of delivered emails that recipients open, a measure of how many people were enticed to look inside. It has long been a headline email metric, especially for judging subject lines, but privacy changes have made it far less reliable than it once was, so it must be read with care.

Open rate sits early in the email funnel: of the emails that reach the inbox, how many get opened? It reflects, above all, whether the subject line and sender earned the recipient's attention. But because of how opens are now tracked, the number is increasingly noisy, and over-trusting it is a common modern mistake.

What open rate measures

Open rate is opens divided by delivered emails, over a campaign or period. Traditionally it gauged the appeal of the subject line, preview text, and sender name, the elements a recipient sees before deciding to open. A higher open rate meant more recipients were enticed to look inside, an intermediate step on the way to clicks and replies.

Why open rate has become unreliable

Opens are typically tracked via a tiny invisible image (a tracking pixel) that loads when the email is opened. Privacy features, most notably Apple's Mail Privacy Protection, now pre-load that image whether or not the recipient actually opens the email, inflating open counts, while other privacy settings can block the pixel entirely, undercounting them. The result is an open rate that is systematically distorted and no longer a precise measure of genuine opens.

Open rate vs click and reply rate

How to use open rate today

Open rate still has uses, but with caveats. It is best treated as a rough, directional signal, useful for relative comparisons (A/B testing subject lines within the same audience and period) rather than as an absolute truth. The trend in measurement is to weight harder signals, clicks and especially replies, which require genuine intent and are far less gameable. Within the broader picture of email engagement metrics, open rate is now a supporting indicator, not the headline.

Why open rate still matters (with caveats)

• Subject-line testing. For relative A/B comparisons in one audience, it still offers signal.
• Deliverability hint. A sudden open-rate collapse can flag a deliverability problem.
• Funnel context. It is one step in the funnel, useful read alongside clicks and replies.
• Trend watching. Big relative shifts can still be informative even if absolute values are noisy.

Common open rate mistakes

• Treating it as precise truth. Privacy distortion means the absolute number is unreliable.
• Optimizing opens over outcomes. A great open rate with no clicks or replies is a vanity win.
• Comparing across distorted populations. Inflated opens make cross-audience comparisons misleading.
• Ignoring the shift to harder signals. Relying on opens while clicks and replies tell the real story.

Open rate measures how many delivered emails get opened, once a headline metric, now a noisy, privacy-distorted one. Used carefully, for relative subject-line testing and as a directional hint rather than absolute truth, it still has value, but the reliable signals of email success are now clicks and, above all, replies.