Open Rate
The share of delivered emails a recipient actually opened.
A weaker signal now that privacy-preserving clients pre-fetch images.
Definition
Open rate is the share of delivered emails a recipient actually opened, tracked when an invisible pixel loads or a tracked link is clicked. It used to be a reliable engagement signal, but privacy-preserving clients like Apple Mail now pre-fetch images automatically, inflating the count and making open rate a much weaker signal than it once was.
We spend most of our time thinking about deliverability, the question of whether a message reaches the inbox at all, so we have watched open rate go from a genuinely useful engagement signal to one senders now have to actively second-guess. It is still on every dashboard, but the number stopped meaning what it used to mean around 2021. Here is how open rate is actually measured, why it once worked, what broke it, and what to watch instead.
How open rate is measured
Open rate is calculated as opens divided by delivered emails, not emails sent, since a message that bounced was never in a position to be opened. The mechanism behind an individual “open” is simple: every marketing email embeds a tracking pixel, a single transparent 1x1 image with a unique URL, in its HTML. When the recipient’s mail client renders that image, it requests the pixel from the sender’s server, and that request is logged as an open.
Some email service providers supplement the pixel with a secondary rule: a click on any tracked link inside the message also counts as an open, on the logic that a click cannot happen without the message having rendered first. In practice this means open rate has always been a proxy built on top of image loading, not a direct measurement of a human’s attention.
Why it used to be a good signal
For most of email marketing’s history, that proxy held up reasonably well. Many desktop and webmail clients did not auto-load images by default, so a rendered pixel generally meant a person had opened the message and either viewed it with images on or explicitly clicked “show images.” That made open rate a workable, if imperfect, way to compare sends against each other: which subject line performed better, which send time got more attention, which segment of a list was still paying attention at all.
Because the underlying mechanic stayed roughly consistent from one email to the next, the trend line was the useful part. Senders used it to catch disengaged segments before they turned into spam complaints, and to validate that a change to subject lines or timing was actually moving the needle.
How Apple Mail Privacy Protection broke it
That consistency ended with Apple Mail Privacy Protection (MPP), which rolled out with iOS 15 and macOS Monterey in 2021. MPP routes all remote images, tracking pixels included, through Apple’s own proxy servers, and Apple pre-fetches and caches every image in a message the moment it arrives in an Apple Mail inbox, for every user who has the feature enabled, whether or not they ever actually open the email.
The effect is that the tracking pixel fires on delivery, not on genuine human attention. Because Apple Mail represents a large share of consumer email opens industry-wide, this pushed average open rates up across the board and flattened them toward a uniform, artificially high baseline. A send that genuinely resonated and one that landed with a thud can now show nearly identical open rates, purely because Apple pre-fetched both the moment they arrived. The signal did not just get noisier. For a large chunk of any list, it stopped measuring engagement at all.
What to track instead
The honest fix is to stop treating open rate as a headline number and lean on metrics that still require deliberate human action. Click rate, and click-to-open rate specifically, survive automated pre-fetching because a click cannot happen without someone actually engaging. Reply rate and downstream conversion or revenue per send tell you even more directly whether a message did its job.
It is also worth remembering that mailbox providers themselves use engagement signals for reputation scoring that are not the same thing you see in your own dashboard. A provider can observe genuine, provider-side behavior — whether a recipient moves a message out of promotions, marks it not-spam, or deletes it unread — none of which routes through your tracking pixel at all. That gap is part of why a sender’s own open-rate number and a provider’s actual view of engagement can diverge sharply.
Underneath all of it sits the metric that actually gates everything else: deliverability. None of click rate, reply rate, or conversion can happen for a message that never reached the inbox. A healthy-looking open rate can coexist with a slowly collapsing sender reputation if a growing share of sends are quietly landing in junk instead. That is why we push teams to verify their list and monitor deliverability directly, rather than trusting a metric that can look fine right up until it isn’t.
Explore more from Verifox
Open rate sits inside a wider set of deliverability concepts. These are the terms most worth understanding next.
Common questions
Open rate, answered
Open rate used to mean something, before Apple started pre-fetching images by default. Here’s what it can still tell you, and where it lies.
What is considered a good open rate?
Before Apple Mail Privacy Protection, 20-30% was a common benchmark for a healthy list, though it varied heavily by industry and list size. That number is far less meaningful today, since a large chunk of Apple Mail opens are pre-fetches, not human reads.
A “good” open rate now depends more on comparing your own sends over time than matching an industry average. A sudden shift is more informative than the absolute number itself.
Why did my open rate suddenly jump?
The most common cause is a shift in your audience’s mail client mix, not a change in how engaging your emails are. If more of your list reads mail on Apple Mail (iOS or macOS), Apple’s privacy proxy pre-fetches the tracking pixel the moment a message lands, registering an “open” before anyone reads it.
A jump can also follow a list-cleaning pass or a verification run, since removing dead addresses raises the denominator quality. Either way, treat a sudden open-rate jump as a signal to check your mail-client breakdown before celebrating.
Is open rate still worth tracking?
Yes, but as a trend line, not a headline number. Comparing this week’s open rate to last week’s, for the same audience mix, can still flag something worth a look, like a broken subject line or a send that landed in spam.
What it can no longer do reliably is tell you whether an individual recipient engaged with a specific email, since a meaningful share of “opens” never involved a human looking at the message.
What’s the difference between open rate and click rate?
Open rate counts a tracking pixel loading. Click rate counts someone actually clicking a link inside the email. A click requires intentional action from a human, so it survives automated image pre-fetching in a way open rate does not.
That makes click rate, and click-to-open rate specifically, a far more trustworthy read on genuine engagement post-2021, even though it naturally runs lower than open rate ever did.
Does Gmail also inflate open rates?
Not to the same degree. Gmail proxies and caches images for bandwidth and security reasons, which can register an open slightly early or without a live view, but it does not systematically pre-fetch every image in every message the instant it arrives the way Apple Mail Privacy Protection does.
The practical effect is that Apple Mail is the dominant source of inflated opens today, so a list skewed toward iPhone and Mac users will show a noticeably flatter, higher open rate than one skewed toward other clients.
What metric should replace open rate as my main KPI?
There is no single replacement, because open rate was never measuring the thing that matters most anyway. Click rate, reply rate, and conversion or revenue per send are all better proxies for genuine engagement, since each requires deliberate action from the recipient.
Underneath all of it sits deliverability: none of those metrics can happen for a message that never reached the inbox in the first place. We’d treat inbox placement and sender reputation as the KPI that actually deserves the top spot on a dashboard.
Can a high open rate hide a deliverability problem?
Yes, and this is the trap. An inflated, Apple-driven open rate can look healthy on a dashboard while a growing share of your other mail quietly lands in junk folders instead of the inbox, especially for recipients on providers that don’t pre-fetch images.
That is why we push senders to verify their list and watch sender reputation directly with the free email checker, rather than trusting a metric that can look fine right up until deliverability quietly collapses.