How to write a subject line

February 11, 2025

Why “Quick question, Will” scores a 96/100 but still lands in SPAM!

Ran a little experiment recently. I tested some popular cold outreach subject lines with an online subject line rater.

“Quick question, Will” scored a 96/100—almost perfect. But if it landed in *my* inbox, I’d delete it in a second.

Scoring well ≠ converting well.

What actually works? Based on what we’ve seen with Rocketbrew:

  • ✍️ 3-4 words is the sweet spot – Shorter subject lines (under 5 words) tend to have higher open rates.
  • ✍️ Personalization beats clickbait– “Quick question” is vague. Instead, make it about them: reference their work, interests, or recent LinkedIn activity.
    • “Your post on AI”
    • “Shoptalk 2025 next month”
  • ✍️ No ‘email-y’ words – Avoid words like "free," "discount," or "meeting request." Instead, make it sound like a note from a colleague.
  • ✍️ Questions work—when specific – Instead of “Quick question”, try:
    • "Scaling your AE team?"
    • "Is [Company] exploring X?"

A subject line’s job isn’t just to get opened—it’s to make answering feel easy.