Numbers tell you what. Analysis tells you why.

Metrics to track:

• Open rate: Primary metric for subject lines
• Click rate: Did the open lead to engagement?
• Unsubscribe rate: Did clickbait damage trust?

Questions to answer:

• What made the winner win?
• Can I apply this insight to future emails?
• What hypothesis should I test next?

Document learnings. Build a swipe file of winners.