Email open rate
Email open rate is the number of opens divided by the number of emails delivered, as a percentage. It is measured by a tiny tracking pixel that loads when the message is viewed. Since Apple's Mail Privacy Protection began pre-fetching images regardless of whether a person opened the email, pixel-based opens are inflated and unreliable, so open rate is now read as a soft signal rather than a precise engagement measure.
What this means
Open rate = opens ÷ delivered emails, as a percentage. An 'open' is recorded when a 1×1 tracking pixel embedded in the message loads from the server, which is taken as a proxy for the recipient viewing the email.
Why Mail Privacy Protection broke it
Apple's Mail Privacy Protection, introduced with iOS 15, pre-loads remote content — including tracking pixels — through proxy servers whether or not the recipient opens the message. That registers opens for emails nobody read, inflating the rate and decoupling it from real attention. Clients that block images do the reverse, under-counting genuine opens.
- Open rate = opens ÷ delivered (pixel-based)
- Mail Privacy Protection pre-fetches pixels, inflating opens
- Image-blocking clients under-count real opens
How to read it now
Because opens are noisy in both directions, treat open rate as directional and corroborate engagement with clicks and on-site behaviour. Comparing open rates over time within one audience is more meaningful than comparing across lists or against external numbers that may predate privacy changes.
How it appears in analytics and logs
A high open rate may reflect genuine interest or automated image pre-fetching by privacy features — without click corroboration it no longer cleanly indicates that people actually read the message.
Diagnostic use case
Read open rate as a directional, increasingly noisy signal of subject-line and sender interest, and lean on click-based metrics where privacy-driven image pre-fetching has inflated opens.
What WebmasterID can help detect
WebmasterID measures what email recipients do after they click through to your site, a first-party signal that is unaffected by mailbox image pre-fetching.
Common mistakes
- Treating pixel opens as a precise read count after MPP.
- Comparing post-MPP open rates to older benchmarks.
- Optimising subject lines on inflated open signals alone.
Privacy and accuracy notes
Open tracking relies on a remote image load tied to a recipient; treat it as privacy-sensitive, prefer aggregate reporting, and read this as educational, not legal advice.
Related pages
- Click-to-open rate (CTOR)
Click-to-open rate (CTOR) is the number of unique clicks divided by the number of unique opens, as a percentage. By using opens rather than deliveries as the denominator, it isolates how compelling the email's content and calls to action were among people who actually opened it. Because the opens denominator is now inflated by privacy-driven image pre-fetching, CTOR has become harder to trust and is read alongside raw click rates.
- Email deliverability rate
Email deliverability rate is the share of sent emails that were accepted by receiving servers — delivered divided by sent, the inverse of the bounce rate. But 'delivered' only means not bounced; it does not say whether mail reached the inbox or the spam folder. True inbox placement depends on authentication (SPF, DKIM, DMARC), sender reputation, and engagement, which is why deliverability is read with placement and complaint signals.
- Click-through rate (CTR)
Click-through rate is clicks divided by impressions, expressed as a percentage. The catch is what counts as an impression: Google Search Console counts a result appearing in search, while ad platforms count an ad being served or viewed. Because the denominator differs by platform, CTR figures are only comparable within the same system — and a low CTR can mean wrong audience or simply low intent.
- Privacy-first analytics
First-party click-through behaviour, no pixels.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.