Should open rate still be used as a KPI?
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As a primary KPI, no. As one signal in a set of metrics, yes, with caveats.
The problem: Apple Mail Privacy Protection pre-loads tracking pixels for Apple Mail users, inflating open rates by 5-20 percentage points for most senders. An open rate that was 25% before 2021 might show 40-45% today, and the increase isn't real engagement. If you're optimizing campaigns based on open rate or setting targets around it, you're working with a number that doesn't mean what it used to.
What to use instead as primary KPIs:
- Click rate: Actual clicks require human intent. Much harder to inflate.
- Click-to-open rate (CTOR): Clicks as a percentage of opens. Even with inflated opens, a drop in CTOR signals declining engagement.
- Conversion rate: Did the click turn into a purchase, signup, or other goal action?
- Reply rate: For personal or plain-text email, the strongest engagement signal of all.
- Unsubscribe rate: A directional signal of list health and relevance.
Open rate is still useful for directional trends within your own data. A sudden drop in open rate is still worth investigating, even if the absolute number is inflated. But setting an open rate target for a campaign and calling it a success if you hit it is increasingly misleading.
Most deliverability-focused senders are shifting to click-based and conversion-based KPIs. That's the right direction.
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