Subject Line Testing

Subject lines are the highest-leverage content decision in any email. They determine whether your email gets opened at all. But testing them properly is difficult: most platforms only let you test 2 subject lines, and results are measured in open rates rather than downstream revenue.

How liftstack handles subject line testing

• Create a subject line snippet with 2–3 variants
• Set open rate as your primary metric for fastest signal (minutes to hours)
• Conversion rate and revenue are still tracked as secondary metrics
• Results typically arrive within hours of sending

A note on open rate accuracy

Apple Mail Privacy Protection inflates absolute open rate numbers. However, relative comparisons between variants remain valid because the noise affects all variants equally. liftstack accounts for this in its statistical model.

Why this matters

Subject line testing gives you the fastest feedback loop in email experimentation. Use it to build intuition about what resonates with your audience, then apply those patterns to higher-stakes tests like hero blocks and CTAs.