Question 1

What makes an email subject line convert?

Accepted Answer

The best subject lines balance curiosity and clarity. Curiosity opens the email, clarity earns trust. Pure clickbait gets opens but tanks reply rate and inbox reputation. Aim for 30–50 characters so the line displays in full on mobile, and pair it with preview text that complements rather than repeats the subject.

Question 2

How long should a subject line be?

Accepted Answer

Aim for under 50 characters. Apple Mail on iPhone shows about 41 characters in vertical orientation; Gmail shows around 70 on desktop and ~30 on mobile. Anything past 50 risks getting truncated mid-thought. Front-load the most interesting word so the visible portion still pulls attention.

Question 3

Should I use emojis in subject lines?

Accepted Answer

Use them sparingly — one well-placed emoji can lift open rate, but stacking them looks spammy and triggers some inbox filters. They work best in retail and lifestyle brands; B2B and luxury brands are usually better off without. Test on your list rather than copying what other brands do.

Question 4

What about preview text (preheader)?

Accepted Answer

Preview text is the second most important conversion element after the subject. Don't waste it on 'View this email in your browser.' Use it to extend the subject's tease, drop in a benefit, or pose a follow-up question. Best preheaders complement, not duplicate, the subject — together they tell a complete story.

Question 5

How do I A/B test subject lines?

Accepted Answer

Test two clearly distinct angles, not minor word swaps. Send each variant to ~10–20% of your list, wait 4–6 hours, then send the winner to the rest. Statistical significance for subject line tests typically requires several thousand opens per arm — small lists should test the most polarized variants for clearer signal. Use our A/B significance calculator to verify your sample size is enough.

Email Subject Line Generator

Email details

Tell us about your email

Frequently asked questions