Blog: What makes a good email subject line?

Here are the key drivers for email subject lines that work - and get people opening your message.

Every marketer knows that the first step to getting results from an email is for the recipient to read it. To maximise open rates, you need to choose a compelling subject line - that's likely the main thing the recipient uses to inform their decision whether or not to open the email.

We've combined our experience putting hundreds of subject lines to the test with real people, plus the experience of email pros, and distilled that into the key things that boost your open rates.

Ready? Here's what makes the best email subject line:

  1. Keep it short. A typical email app shows 50-60 characters of an email’s subject line and on a mobile phone it may be as few as 25 to 30 characters. Keep things punchy and aim for 5 to 7 short words.
  2. Put the most important info first. If your recipient is on a mobile, the latter parts of the subject might be cut off - so start with the key information.
  3. Make it all killer and no filler. Skip prepositions, greetings, and platitudes - no to "hello", "thanks" or other flab. Focus on verbs (the "doing" words) and make them seem vital.
  4. Eliminate filler words. With such precious space, don’t waste it with unnecessary words like “hello,” “nice to meet you,” and “thanks,” which can easily be included in the email’s body.
  5. Be specific. What is the one thing the reader will get from the message? Put yourself in their shoes and tell them quickly what's in it for them.
  6. Think about specific words. Some email pros will be using filters to help organize their mailbox, so make sure that relevant key words are included in your subject so the message makes its way into the right box.
  7. Say if you need an action or a reply. Save peoples' cognitive effort by making clear what you want them to do; for example, include "FYI" if the email is just for their information, or start the subject with "Action Needed" if you need them to do something.
  8. Set a deadline. Time pressure is a powerful tool, whether for promotional emails or for messages you send to potential clients or recruits. Make it clear that what you're offering in the message is only available for a limited time.
  9. Personalize. Messages that start with the recipient's name, or with their company's name, can prove more likely to be opened - but only if the information within is truly specific to that recipient. Otherwise it can seem like a cheap trick. So use with care!
  10. Don’t start a sentence and finish it in the email body. It might seem clever but most people find this annoying. You run the risk of the recipient deleting the message without opening it.
  11. Check and check again. Simple spelling mistakes or copy-paste errors make you look dumb and get your emails deleted instead of read. So take a couple of minutes to check your email subject line before you hit "Send."
  12. Avoid using ALL CAPS. It might grab someone’s attention, but in the wrong way. It’s the digital equivalent of yelling, which isn't respectful of your reader. Even worse, it's likely to increase the SPAM score of your message so it might not reach their inbox.
  13. Use questions. A smartly crafted subject line can leave the reader intrigued enough to open the message for the answer. So tease your recipient and use questions to set you up for a high open rate.
  14. Test, test, and test again. You can't expect to know everything in every situation. So use A/B testing to send several variants of your email subject line to check response amongst a smaller group first. Even better, try our advanced email subject testing tool to pre-test potential subject lines with real people before you send a single message.

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