Subject Line Best Practices: 4 Tips to Boost Your Email Open Rate

Just in time for email season (AKA all year long), we’re sharing some subject line best practices to help you increase open rates. After all, the more people who open your emails, the more people who can click through on those nurture streams, promo offers, and newsletters.

Follow these five best practices for email subject lines to pique interest so recipients open the email to learn more.

1. Highlight the WIIFM

People typically open an email because of an “ooh moment.” One of the most effective ways to create these moments is by featuring the WIIFM (“what’s in it for me?”) in your subject line. 

For instance, if you’re sending a promo, mention something like “save 30%.” That little phrase achieves two critical goals: be clear and be compelling. Right away, the reader knows benefit awaits and has reason to keep reading.

Some tactics you can use to grab attention with your subject line: 

  • Relevancy – Speak to the reader’s goal or mindset, like their business challenge for a sales email
  • Urgency – Show there’s a reason to open now, such as a limited time offer or seasonal reference
  • Personalization – Include dynamic fields, like first name, company name, or geo, to bump up relevancy
  • Curiosity or surprise – Hook readers by teasing a mystery or saying something unexpected 

For some inspiration on focusing on the WIIFM, check out these real-world subject line examples collected by Hubspot.

2. Keep it brief

In general, shorter subject lines are better, especially for mobile users because less screen size requires truncating longer subject lines. When in doubt, write for mobile first.

A common best practice for subject line length is around 40-50 characters. This lets you get across key and compelling info, while avoiding the hard cutoff in mobile inboxes. If you need everything in a longer subject line, frontload the most important info.

Source: Campaign Monitor

Also, look for redundancies. That save 30% subject line above doesn’t also need to mention that there’s a sale or discount involved, as that’s already implied. You could use that same space to mention a popular item or category instead.

3. Use preheaders to build, not repeat, info

Preheaders, sometimes called preview text, give you a chance to choose the additional text that accompanies subject lines in inboxes. Most CRM platforms allow you to customize this field. 

The big tip here is to have your subject line and preheader text work together. One of the biggest lost opportunities we see with emails is repeating the same information in both spots. 

Think of your subject line as a way to grab attention and your preheader text as a way to build on that opener. One element should include a call to action, which can be overt (preheader = “Open to…”) or a bit more subtle but still active (subject line = “Discover how…”). Either way, use action-oriented words to encourage reflexive clicks. Just be sure to avoid words that can trigger spam filters.

4. Test your subject line strategies & tactics

Testing your approach to subject lines (and preheaders) is key to optimizing open rates. These real-world insights help you iterate on email performance, both in the near and long term. 

For a sophisticated yet accessible way to iterate and learn over time, try our “Testing, testing, 1-2-3” approach.

  1. 10/10/80 split testing – Send 10% of your list one subject line and another 10% a different subject line, then send the remaining 80% the winner
  2. A/B testing – A simple, clean test where you compare changing only one variable between two subject lines (e.g., including an emoji vs not or using sentence vs title case)
  3. Multivariate testing – A more advanced test requiring pretty significant list size, where you can test and track multiple variables cleanly
Source: Zapier


With our five subject line best practices, you’re well on your way to boosting your email open rates. To learn more about how Expand can help you write and design emails (and the optimized website to drive conversion, fill out the contact form below.

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