Click-to-Open Rate: When It Beats Click-Through Rate

Use the click-to-open rate when you want to judge an email’s content and design. Use click-through rate when you want to judge the campaign as a whole. Simple enough, right? The trouble starts when your manager wants one engagement number and the two metrics disagree. And then there’s Apple Mail Privacy Protection, which now distorts one of them (more on how that happens further down).

What Are Click-Through Rate and Click-to-Open Rate?

Click-through rate (CTR) divides clicks by the number of emails delivered. Click-to-open rate (CTOR) divides clicks by the number of opens. Both are standard email engagement metrics, and the math looks like this:

• CTR = unique clicks / delivered emails x 100
• CTOR = unique clicks / unique opens x 100

“Unique clicks” means the same thing in both formulas. Someone who clicks three times still counts once. So the only real difference is the denominator: the number you divide by, or put another way, the group of people you measure the clicks against.

CTOR vs CTR: Which Question Does Each Metric Answer?

CTR tells you how well the whole send turned your list into clicks. CTOR tells you how convincing the email was to the people who actually opened it. That’s the short version. The click-through rate of an email lumps a lot together: list quality, deliverability, the subject line, the content. CTOR strips out the subject line and inbox placement, and what’s left is the body of the email. Copy, offer, layout, the call to action (CTA). But each metric has a blind spot:

• CTR can’t tell you whether a weak result came from the inbox or from the message itself.
• CTOR says nothing about the people who never saw the email at all.
• Neither one tells you whether those clicks led to a sale or a reply.

When Does Click-to-Open Rate Beat Click-Through Rate?

CTOR wins whenever you’re comparing the content of emails and the open data behind them is stable and reliable. In practice, that usually means:

• testing two versions of the email body,
• comparing CTA placement or layout,
• checking whether a template redesign actually worked,
• comparing content across segments that open emails at different rates.

Running A/B testing email campaigns on the body copy? Then CTOR shows you which version persuaded readers better. Flip it around for subject line tests, send-time decisions or list health. There you want CTR, or the open data itself. Why? Because those are exactly the effects CTOR hides.

How Apple Mail Privacy Protection Skews Click-to-Open Rate

Mail Privacy Protection can record opens that never happened. That inflates the CTOR denominator and drags the ratio down. According to Apple’s Mail Privacy Protection page, Mail downloads remote content in the background by default, whether or not you engage with the email. It also sends that content through two separate relays, so senders can’t find out when or how many times you opened a message.

Clicks are different. A click still needs a real person to do something, so click counts stay tied to actual behaviour. That’s why the click rate after Apple Mail Privacy Protection holds up better than any ratio built on opens.

Open rates took the hardest hit. The story of why open rates went up shows how background downloads turned a behavioural signal into a technical one. What does that mean for you day to day? You can’t compare CTOR directly across the periods before and after MPP. Same problem with lists that have different shares of Apple Mail users.

Which Email Engagement Metric Should You Report to Your Manager?

Report CTR as your headline number and keep CTOR next to it as a diagnostic. Never on its own. My advice is a simple routine:

1. Lead with CTR and the absolute number of clicks.
2. Add CTOR only when you’re comparing content within the same list and time period.
3. Say plainly that privacy features inflate open counts.
4. Tie clicks to outcomes like conversions or replies.

In MailCraft, campaign reports with click tracking show clicks for each campaign next to opens, so both figures sit in one view. One thing, though: don’t put the two metrics in a single trend chart. A rising line and a falling line on the same axis will confuse anyone who skims it (and most managers skim).

The click-to-open rate is a great tool for judging content. As a headline number, though, it’s weak while opens stay unreliable. Pick your metric by the question you’re answering, not by whichever one looks better this month. Once you’ve made that call, the campaign analytics guides go deeper on reading campaign results.

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