Data quality · 7 min read
Why Email Open Rates Can Be Misleading
Understand image proxies, blocked images, automated requests, denominator choices, and safer ways to interpret email open rates.
Updated October 23, 2026 · Definitions and caveats are stated in the text.
An open rate is a ratio built on a fragile event
A rate is only as meaningful as its numerator, denominator, and collection method. An email open rate usually divides some version of tracked opens by a send or delivery count. If an image request is automated, hidden, cached, or blocked, the numerator no longer corresponds cleanly to human readers. If the denominator mixes sent, accepted, delivered, or suppressed messages, the rate changes meaning again.
Before comparing two reports, write down exactly what each side counts. 'Opens ÷ delivered messages' is not interchangeable with 'open requests ÷ attempted sends,' and neither is a direct measure of reading comprehension or purchase intent.
- Keep raw requests separate from estimated unique opens.
- Name the denominator in the report label or note.
- State how duplicate requests, retries, proxies, scanners, and missing provider data are handled.
Privacy features can move the number in either direction
A privacy relay may fetch remote images without a person opening the email at that moment. Conversely, a reader who blocks images may not generate a request. Caching can reduce repeated requests. Security systems may fetch links or images before delivery to the inbox. These behaviours can inflate, suppress, or shift the timing of measured events.
Classifiers are heuristics, not proof. A report should preserve uncertainty rather than claim it can perfectly identify a human from a user-agent string or proxy address. Do not fingerprint recipients or infer identity from network signals.
Choose a better decision signal
For delivery questions, use verified provider events and a provider-supplied sent denominator. For content interest, look at tracked link clicks while separating automated traffic where supported. For business outcomes, measure a conversion on the destination site with a documented attribution window and consent policy.
A click still does not prove that a person read the destination page, and a conversion may be influenced by other channels. Triangulate signals and describe limitations. If a metric requires a provider connection you have not configured, show 'Requires integration' or 'Not available'—not a guessed rate.
Questions
Should I stop looking at open rates?
You can keep them as a low-confidence diagnostic if the collection method is disclosed. Avoid using them alone for delivery, revenue, or individual-level decisions.
What should I compare instead?
Choose the signal that matches the question: verified provider events for delivery, classified clicks for link interaction, and consent-aware destination events for website outcomes.
Official references
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