Subject Lines

Email subject lines serve as a first – and sometimes last – impression of a communication and can mean the difference between a successful campaign and low open rates.

Overview

The subject line is one of the most critical elements of an email. It’s the first impression in the inbox—and often the deciding factor for whether your email gets opened or ignored. A good subject line is clear, relevant, and compelling without being clickbait.

Best Practices

Be Clear Before Clever

  • Prioritize clarity over wit, especially in transactional or informational emails
  • Ensure the value or purpose is immediately understandable

Keep It Concise

  • Aim for 35–50 characters or less
  • Short subject lines display better on mobile and grab quicker attention
  • Don’t lie or mislead

Lead with What Matters

  • Put the most important words at the beginning
  • Avoid burying keywords behind filler text or brand names

Create Curiosity or Urgency (When Appropriate)

  • Use timely language to encourage action (for example, “Last chance to register”)
  • Ask a question or tease the content without misleading
  • Include deadlines/offer end dates

Avoid Spam Triggers

  • Don’t use excessive punctuation, all caps, or misleading phrases like “FREE!!!”
  • Avoid words like “guaranteed,” “risk-free,” or “act now” when not genuinely warranted

Tone and Voice Alignment

  • Match your brand’s tone (for example, professional, playful, supportive)
  • Ensure subject lines reflect the content of the email—no bait-and-switch
  • Personalize when appropriate (for example, use the recipient’s name or reference behavior)

Accessibility and Internationalization

  • Use simple, readable language
  • Avoid idioms or wordplay that may not translate well
  • Consider character limits in different languages when localizing

Testing and Optimization

  • A/B test subject lines to measure performance
  • Track open rates and engagement over time
  • Adjust based on audience behavior, segment, and email type
  • Exclamation vs questions (where appropriate)
  • Numbers and % – for example, Top 10 tips, 3 Good Reasons…
  • Length of subject lines – for example short vs longer (but not too long!)
  • Emotive words – for example, Wonderful, Heavenly, Magical (where appropriate)
  • Benefit and experiential words
  • Use emojis…with caution!

Questions?

Connect with the DLS Team on Slack or by email.

Resources

Check out additional resources.