What Is Open Rate?

Open rate is the percentage of delivered emails recorded as opened, calculated as unique opens divided by emails delivered. Tracking works by embedding an invisible one-pixel image in the email; when a recipient's client loads that image, an open is logged. The metric has become unreliable. Apple Mail Privacy Protection, launched in 2021, preloads images for its users and registers opens whether or not anyone read the email, while corporate security scanners trigger false opens and image blocking hides real ones. In cold email there is an additional problem: the tracking pixel itself adds a fingerprint that spam filters can associate with bulk sending, so many cold email senders disable open tracking entirely to protect deliverability. As a result, open rate is best treated as a directional deliverability signal rather than a measure of interest — reply rate is the metric that reflects actual engagement.

Open Rate in Practice

When open tracking is enabled and deliverability is healthy, cold email open rates of 40-70% are common; a sustained figure below roughly 30% usually means messages are landing in spam rather than that subject lines are weak. That is the practical use of the metric: a smoke alarm for placement problems, checked alongside inbox placement tests, not a KPI to optimize. The common mistake is chasing opens directly — writing clickbait subject lines that inflate opens but attract fewer and worse replies, or comparing open rates across mailbox providers as if the numbers were measured the same way post-MPP. A second mistake is leaving tracking on by default: on a fresh sending domain doing 25 emails per mailbox per day, the marginal data from opens is rarely worth the deliverability risk of the pixel. Most experienced cold email operators run open tracking briefly to validate placement, then turn it off and manage campaigns on reply rate.