Resources Hub » Blog » The Ultimate Email Subject Line Testing Checklist

Email subject lines are always on the minds of email marketers. Because they are tied directly to open rates—and people actually seeing your emails in their inboxes—email subject lines should always be tested, optimized, and improved.

We hope this list helps you brainstorm and optimize your email subject lines. Don’t take this list as a series of steps to take every subject line through. Instead, use this as a catalyst for your brainstorming, and then A/B test your different subject line ideas to see what your audience responds to best.

Shake up your go-to subject line and start testing out some variations using this list.

Email Subject Line Testing Checklist

Formatting options

Title case: All lowercase letters, sentence case, and weird capitalization.

  • we made this ebook for you
  • We made this ebook for you
  • We made this ebook for YOU

Length: A few words, short, longer, or running off the screen.

  • New shorts are here.
  • Don’t miss these new summer shorts.
  • We have shorts that are perfect for your summer style.
  • Looking to stay cool this summer? We have the answer, but we’ll keep it short.

Word order: When sending an A/B test, try flipping the clauses of your sentence.

  • Create masterpieces in the kitchen with this pan.
  • Use this pan to create masterpieces in the kitchen.

Tone approaches

Urgency: Add or remove a sense of urgency to your subject line.

  • Last chance to buy these tickets.
  • Plenty of tickets for you to buy.

Authority: Try expressing either authority or friendliness.

  • All your insurance questions answered.
  • Need help answering your insurance questions?

Wit: Make your subject line informational, or try making it clever.

  • Learn how to travel light in today’s webinar.
  • Leave the extra shirt behind for today’s webinar.

Active / Passive: Experiment with using either active or passive voice.

  • Hamburgers are ready to be eaten in Nashville.
  • You’re all set to eat some burgers in Nashville.

Literary devices: Use alliteration, rhyming, isocolon, hyperbole, etc.

  • Big brew gets creative with this bold buy.
  • A recent acquisition brings big brew closer to you.
  • Big brew. Big buy. Big news.
  • Biggest news from Big Brew in 2018.

Style of presentation

Unique news: Try out an invitation or announcement.

  • You’re invited to our private webinar.
  • Just announced: private webinar for exclusive participants.

Statements: Thank you’s, questions, or how-tos.

  • Thank you for shopping with our company.
  • Did you enjoy your shopping experience?
  • How to make the most out of your shopping experience.

List: Try adding a number to your subject line.

  • 4 things people are saying about our headphones.

Trending: Use words that insinuate timing.

  • The latest on green candies.
  • This week’s hottest green candies.

Statistics: Pull a stat from your content into your email subject line.

  • 63% of you won’t open this email.


Personalization: Add automatic personalization like first name, full name, or location.

  • Amazing restaurants near you, Frank.
  • Amazing restaurants in Nashville.

Number of topics: Try including one piece from your email versus multiple.

  • Mix drinks have more sugar than ever before.
  • Sugary mix drinks, summer cocktails, and staying hydrated.

Focus: The problem, the solution, or the way to address either.

  • Mice are getting into your crawl space.
  • We can keep the mice out of your house.
  • Our trapping technique eliminates mice once and for all.

Emojis: Try adding an emoji (or two) to your subject line.

  • ? Good times ahead of you
  • ⭐ The best news for your week ⭐

Industry: Segment based on industry and address that group specifically.

  • Bright, lasting paints for your remodeled bedroom.
  • This paint holds up to any contractor’s needs.
  • Painters report: this paint is easy to apply and easy to clean up.

Wrap up

Your email subject lines have never looked better! Make sure you bookmark or save this list for future creative reference. You’re never done testing email subject lines. There’s always room to improve your open rate and email engagement.

This list is a perfect pair for your email service provider’s A/B test capabilities. Test everything you can think of and see what’s right for your audience!

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This blog provides general information and discussion about email marketing and related subjects. The content provided in this blog ("Content”), should not be construed as and is not intended to constitute financial, legal or tax advice. You should seek the advice of professionals prior to acting upon any information contained in the Content. All Content is provided strictly “as is” and we make no warranty or representation of any kind regarding the Content.
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