Open rate is the percentage of delivered emails that are opened by recipients. It is calculated as:
Open Rate = (Unique Opens / Emails Delivered) x 100
If 10,000 emails are delivered and 2,500 are opened, the open rate is 25%. Open rate is the first engagement metric in the email funnel - before a subscriber can click, convert, or buy, they have to open. It measures whether your subject line and sender reputation are compelling enough to earn attention in a crowded inbox.
Average e-commerce email open rates typically fall between 20-30%, with significant variation by segment and email type. Automated flows consistently outperform broadcast campaigns: abandoned cart emails average 40-50% open rates, post-purchase flows 35-45%, and welcome series 40-60% for the first email. Broadcast campaigns (newsletters, promotions) to unengaged lists often fall to 15-20%. The most meaningful benchmark is your own historical rate by segment and email type - industry averages aggregate too many different list quality levels to be useful as targets.
Apple's Mail Privacy Protection (MPP), introduced in iOS 15 in 2021, fundamentally changed what open rate measures. MPP pre-loads email tracking pixels for Apple Mail users - even if they never actually open the email - which records a false open. For brands where 40-60% of subscribers use Apple Mail, this inflates reported open rates significantly and makes the raw metric unreliable as a measure of actual engagement.
The practical response is to treat open rate as a directional signal rather than a precise metric, and to weight click-to-open rate (CTOR) - the percentage of openers who click - more heavily as the primary engagement metric. CTOR is not affected by MPP because it measures actual clicks, not pixel fires. Revenue per email sent is the most reliable email performance metric of all, as it reflects actual downstream behaviour.
Open rate is primarily driven by three factors. Subject line is the most direct lever - length (under 50 characters performs best on mobile), specificity, personalisation (using the subscriber's name or purchase history), and curiosity all lift open rates in consistent A/B testing. Sender name and reputation - subscribers are more likely to open from a recognisable sender name than a generic brand address. Send timing has modest impact; Klaviyo's Smart Send Time feature uses individual subscriber data to predict optimal timing, which typically outperforms fixed-time sends by 5-10%.
List health is the underlying driver of all three. A list full of disengaged subscribers suppresses open rates, damages sender reputation, and ultimately affects deliverability - which reduces how many emails reach the inbox at all. Running regular segmentation to suppress unengaged subscribers (those who have not opened in 90-180 days) and an active sunset flow to remove permanently inactive contacts are the most important list hygiene practices for maintaining strong open rates over time. Sending fewer emails to more engaged subscribers consistently outperforms sending more emails to everyone.
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