A Subject-Line A/B Test That Actually Tells You Something

A Subject-Line A/B Test That Actually Tells You Something
Most 'tests' compare two lines on 50 sends and call a winner. That's noise. Here's a real protocol.

— Pick ONE variable to test: length, question vs statement, or personalized token. Not all three.
— Split a minimum 400-contact segment 50/50. Smaller and your confidence interval is useless.
— Measure on reply rate, not open rate — Apple MPP fakes opens.
— Run the full sequence before judging; subject affects step-1 opens only.
— Log winners in a swipe file with the segment they won on.

Pros
— Statistically defensible results
— Builds a persona-tagged subject library over time
Cons
— Needs volume most small senders don't have
— Reply-rate signal is slow to accumulate

Verdict: Smartlead and Instantly both auto-split, but the discipline is on you. 4/5.

Who it's for: Senders with 400+ contacts per segment who want signal, not vibes.