Best Practices for Email Subject Lines

Our Research team analyzes the emails sent from users through MailChimp to find what practices result in the best open rates. The best email subject lines are usually short, descriptive, and provide the reader with a reason to open your email. Splashy or cheesy phrases don’t help increase open rates. In fact, we’ve learned that many subscribers ignore that type of subject line.

In this article, you’ll find some general tips to keep in mind when you write subject lines, and learn about a few tools you can use to make your subject lines more engaging.

Tips for Subject Lines

  • Avoid Sales or Overused Words
    Most people know to avoid words like "free" in their subject lines because they trigger spam filters. But you should also avoid common words that are associated with sales, like “help,” “percent off,” or “reminder.” These words don’t always trigger a spam filter, but many subscribers will ignore them.
  • Include Localization
    Personalize a message with a recipient's first or last name to improve open rates. MailChimp research suggests including a city name is even better.
  • Use Different Subject Lines
    Newsletters tend to start with high open rates, but these decrease over time. Keep your content fresh, and don’t repeat the same subject line for each campaign. If subscribers can’t tell something about your content from the subject line, they probably won’t open your campaign.
  • Keep Subject Lines Short
    Most people quickly scan subject lines to decide if they’ll open or ignore the email, so don’t expect subscribers to dig through your subject line to figure out if they’re interested. Keep your subject line to 50 characters or fewer.
  • Tone Down Promotional Emails
    Keep the message straightforward and avoid splashy promotional phrases, phrases in all capital letters, or exclamation marks in your subject lines. Subject lines framed as questions often perform better.

Customize Subject Lines

Our emoji picker and merge tags allow you to create a subject line that is fun and personalized.

Emoji Picker

To add emojis to your subject line, follow these steps.

  1. Navigate to the Setup step of the Campaign Builder.
  2. In the Email subject field, click the Smile icon and choose the emojis you want to include.
    Screen of subject line field, with cursor over smiley icon to display emojis.

Not all inboxes render emojis in the same way. Test your campaign or use the Inbox Inspector to view your campaign in several inboxes before you send.

Merge Tags

Use merge tags to personalize the subject line with content that is unique to your subscribers. For example, if you have a field in your list for the city where your subscribers live, use the city merge tag in the subject line and we’ll replace it with each subscriber’s city when the campaign is sent.

We don’t, however, support the use of conditional merge tags in subject lines. It’s always a good idea to test your merge tags before you send your campaign.

Test Subject Lines

MailChimp offers tools to help you write and test effective subject lines. Our Subject Line Researcher uses our extensive collection of subject line data to help you write a subject line, and A/B Testing Campaigns test the performance of up to three different subject lines.

Subject Line Researcher

Our free Subject Line Researcher tool tests different keywords to help you write an effective subject line. To use this tool in the Campaign Builder, follow the steps below.

To use the Subject Line Researcher, follow these steps.

  1. Navigate to the Setup step of the Campaign Builder.
  2. Click the How do I write a good subject line? link under the Email subject field.
    Cursor clicks the How do I write a good subject line link.
  3. In the pop-up modal, click Subject line researcher.
    Screen of modal with cursor clicking the Subject line researcher option.
  4. Type several phrases into the Subject line terms field and click Search to populate results. For best results, enter one term or phrase per line and limit phrases to three words and keep the search broad.
    Screen of Subject Line Researcher with terms to test typed in the subject line terms field.
    MailChimp compares those terms to all subject lines ever used in our system, and displays a 5-star rating system for how the subject lines containing those terms performed.
    Screen of the results from the Subject Line Researcher test showing star ratings for the performance of each option.

Create an A/B Testing Campaign

Unlike the Subject Line Research tool, which tests your subject line against all subscribers on MailChimp lists, A/B Testing Campaigns test your actual subscribers to see what they like best.

A/B Testing Campaigns create up to three versions of your campaign to test how a small difference impacts campaign performance. Send two or three versions of your campaign with different subject lines to randomly selected parts of your list, and we’ll automatically send the campaign with the best open rate to the remainder of your list.

Other Factors that Affect Open Rates

It’s not just your subject line that affects your open rates. Sending frequency, sender, and the nature of your content all impact your results. Here are some things to consider when you create your campaign.

  • Balance List Quality and Send Frequency
    The success of your campaign depends on how well you maintain the interest of your subscribers over time. Create content, including subject lines, that engages your subscribers and meets their expectations. Avoid frequent sending that can overwhelm subscribers and decrease open rates.
  • Set Subscribers’ Expectation When They Opt In
    If subscribers signed up to receive updates about your company, don’t send an email with a subject line like, “10% Discount! Open Now!” On the other hand, if your subscribers specifically opted in to receive discounts and promotions, there’s nothing wrong with saying there’s a coupon inside.
  • Consider the From Name
    The from name can be as important as the subject line, because subscribers won’t open emails from people they don’t recognize. Use the from name to say who you are as the sender, and keep it consistent over time.
  • Use Groups and Segments for Your List
    Target subscribers with groups and segments so they get information that’s relevant to them. If your subscriber data indicates that someone is interested in vegetarian recipes, they probably won’t open an email with a subject line about the 10 best meat recipes. If subscribers provide information to help target your messages, use it.

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