Curiosity subject line: +12.7% opens but fewer unique clicks
Test run byMarketingExperimentsResearch publisher
Commentary byLiftArchiveOur analysis, not theirsA curiosity subject line raised opens by 12.7% on a MarketingSherpa case-study email but got a lower unique clickthrough rate than the plain, results-led subject line.
MarketingExperiments (MECLABS) ran the test on the MarketingSherpa Email Marketing Newsletter list.
Because clicks were the real goal, the curiosity line lost and MECLABS stayed with its straightforward style.
- Unique open rate: +12.7% for the curiosity subject line.
- Unique clickthrough (delivered to click): lower for the curiosity line, even though more people opened it. The size of the drop was only shown in a chart image.
- Verdict: a loss. The variant won the vanity metric and lost the one that mattered.
Control
A straightforward subject line that stated the article's result: 'How Blockbuster Express grew its email list 300%'.
Variant
A curiosity subject line: 'If Alfred Hitchcock wrote emails, could he grow an audience by 300%?'
Why it likely lost
Our reading of the result, not the practitioner's claim.
- The plain subject line made a clear promise about what the reader would get, so the people who opened it were ready to read the case study.
- The curiosity line drew opens from people who were intrigued but not interested in the topic, and the email didn't match what they hoped to find.
- Opens are an early signal. A subject line that inflates them can still send fewer people to the content.
Caveats: Only the open-rate lift is given as a number; the clickthrough drop is shown in an image, and list size was not shared. This is one test on one newsletter from 2012.
Who ran it
MarketingExperiments ran this test and published the results (MarketingExperiments). The numbers are theirs; the summary and commentary on this page are ours.
Read the original case study on MarketingExperiments →
How to run this test on your site
- Hypothesis
- If we use a subject line that states the article's concrete result instead of a teaser, then more subscribers will click through because the promise in the inbox matches the content.
- Primary metric
- Unique clickthrough rate (delivered to click)
- Guardrails
- Unique open rate
- Unsubscribe and spam-complaint rate
- Who should test it
- Content and B2B newsletters whose goal is getting readers to an article or offer. If your only goal is opens, for example for a deliverability warm-up, the result may not apply.
Questions
Do curiosity subject lines work?
They can raise opens, as this test did by 12.7%.
Here they also cut clickthrough, so judge them on clicks or conversions, not opens.
What metric should decide a subject line test?
Use the action you want after the open, such as unique clicks from delivered emails.
Open rate alone can pick the wrong winner.
Are misleading subject lines risky?
Yes. The source argues that subject lines which don't match the email break trust with subscribers and can lead to unsubscribes or spam reports.