Open rate is the metric most email marketers lead with. It's also one of the least reliable metrics in email marketing right now, and has been since September 2021.
Here's what happened, what it means, and which numbers are actually worth your attention.
What Happened to Open Rate
In September 2021, Apple rolled out Mail Privacy Protection (MPP) with iOS 15. When enabled, Apple's mail servers pre-fetch email content, including the tracking pixel used to record opens, before the user actually opens the email.
The result: every email sent to an Apple Mail user on MPP appears as "opened," whether or not the person ever looked at it. In Australia, Apple Mail accounts for around 50–60% of email client usage. Which means a significant portion of your "opened" emails were never actually opened by a human.
Your open rate went up when MPP rolled out. Your actual readership probably didn't.
So What Does Open Rate Actually Tell You Now?
For non-Apple clients (Gmail, Outlook, Android mail apps) open tracking still works. For Apple Mail users with MPP enabled, it's meaningless.
Open rate is now a blended metric: real data from some segments, inflated data from others. The ratio depends on your list's email client breakdown. If most of your subscribers use Apple Mail, your open rate is mostly phantom opens.
This doesn't mean open rate is completely useless. Dramatic drops in open rate can still signal deliverability problems or list health issues. But as a measure of engagement or campaign performance, it's no longer reliable enough to optimise around.
The Metrics That Still Tell the Truth
Click-through rate (CTR)
The percentage of recipients who clicked any link in the email. Clicks require a human to actually interact with the email, so this metric isn't affected by MPP. It's a direct signal of engagement with your content.
Click-to-open rate (CTOR)
Clicks divided by opens. This is more affected by MPP inflation, but for non-Apple segments it's still useful for comparing email content performance. Use it directionally, not as an absolute.
Conversion rate
Of the people who clicked, how many completed the desired action? This requires connecting your email platform to your website analytics or CRM. It's more work to track, but it's the metric that connects email activity to business outcomes.
Revenue per email sent
For ecommerce or any business where you can track transactions back to email campaigns: total revenue divided by number of emails sent. This is the most direct measure of email marketing effectiveness.
Unsubscribe rate
A rising unsubscribe rate is a clear signal that content frequency or relevance has shifted. This metric is unaffected by MPP and remains a reliable negative signal.
Why Revenue Might Be Flat Even When Engagement Is Real
Even if your CTR is healthy, revenue from email campaigns can underperform for reasons unrelated to the emails themselves: the offer isn't compelling, the landing page isn't converting, the product availability changed, or the segment receiving the email is the wrong audience for that particular offer.
Email marketing doesn't exist in a vacuum. A well-written email sent to the right segment with a clear offer pointing to a functional landing page tends to produce results. Remove any one of those elements and the others can't compensate.
What to Do Instead of Optimising Open Rates
Set up proper click tracking in your email platform and connect it to GA4 via UTM parameters. This lets you see what email traffic actually does when it arrives on your site.
Shift your subject line testing focus from "what gets opened" to "what gets clicked." A subject line that creates genuine interest will still drive behaviour you can measure. A subject line that just increases phantom opens from MPP doesn't.
Clean your list regularly. Remove subscribers who haven't clicked anything in 6–12 months. Smaller, more engaged lists produce better deliverability and more reliable metrics. They also cost less to send to.
Frequently Asked Questions
Should I disable open tracking entirely?
Not necessarily. Even inflated open rate data has some use for deliverability monitoring: a sudden drop often signals spam filter issues before other metrics catch up. Keep tracking it, but stop using it as your primary performance indicator.
How do I know what email client my subscribers use?
Most email platforms (Kit, Klaviyo, Mailchimp) provide email client reports under engagement or subscriber analytics. Check this before drawing conclusions about how affected your particular list is by MPP. If 70% of your list uses Gmail, MPP is less of a problem for you than it is for someone with a predominantly iOS audience.
Our open rates went up after a recent campaign. Should we be excited?
Cautiously. Check whether clicks also went up proportionally. That's the more meaningful signal. If opens are up but clicks are flat, the most likely explanation is more Apple Mail users on your list, not better engagement.
