Question 1

What is the best length for an email subject line?

Accepted Answer

Thirty to fifty characters. Long enough to be specific, short enough to survive mobile truncation, where more than half of opens happen.

Question 2

What words trigger spam filters in subject lines?

Accepted Answer

Classic offenders include free with exclamation points, act now, guaranteed, limited time, and all-caps words. The tester flags every trigger it finds and shows you exactly which rule fired.

Question 3

Do lowercase subject lines get more opens?

Accepted Answer

Often, yes, in cold outreach. A lowercase subject reads like a note from a person rather than a campaign from a tool, which is why the scorer gives a small bonus for it.

Your subject line gets judged in half a second.

Common questions