As a rule of thumb, for routine messages, the sentence length should be no more than

A successful email starts with a subject line that grabs the attention of your recipients. Good subject lines are often personal or descriptive, and give people a reason to check out your content. Whatever your approach, it's important to keep your audience in mind, and test different words and phrases to see what they prefer.

In this article, you'll find tips for writing strong subject lines, and learn ways to test subject line performance.

Tips for subject lines

Our Research team analyzes emails sent by users through Mailchimp to find what practices result in the best open rates. Some types of subject lines have proven to be more successful than others.

Here are a few strategies for you to try out.

Add personalization

Use merge tags to personalize your subject lines with each recipient's name or location. Personalization is shown to increase open rates for most users, and may work well when combined with targeted automations such as birthday deals and post-purchase follow-ups.

Getting Started With Merge Tags
Merge Tags for Personalization

Be descriptive

Sometimes, it's better to be direct and descriptive than trendy. Seasonal slogans such as "Fall into savings" or "Sizzling summer bargains" are popular but don't offer a specific hook. Instead, try to communicate the benefits of your promotions, or call attention to specific deals.

Keep it short

For many recipients, especially those reading your emails on mobile devices, shorter is often better. We recommend you use no more than 9 words and 60 characters.

Limit punctuation

Our research shows that it’s best to use no more than 3 punctuation marks per subject line. Too many punctuation marks can make your email look like spam, especially if you use a lot of special characters.

Use emojis carefully

Our built-in emoji picker is a fun and easy way to add some visual pizazz to your subject lines. However, there are a few things to keep in mind when you use emojis.

• According to our research, you should use no more than 1 emoji at a time.
• Use emojis to supplement words rather than replace them, to make sure your main message gets across.
• Different operating systems render different versions of emojis, so it’s important to test.

Test subject lines

There are a few ways to learn whether your subject line is a likely winner: Check out the tips in our built-in subject line helper, view your recent subject line performance, or use an A/B or Multivariate testing campaign to see if different subject lines affect your open rates.

Subject line helper

Our subject line helper checks to see whether your subject line follows our tips around best practices, which are based on the open rate performance of hundreds of millions of emails in Mailchimp.

We’ll display a green check mark for each tip you follow. If your subject line conflicts with one of our tips, we’ll show an alert and suggest what you should change.

Recent subject line performance

For additional help, click the recent subject lines link to view a list of your last 5 subject lines along with their open rates.

A/B and Multivariate testing

A/B and Multivariate tests reveal how small differences impact performance. Unlike the subject line helper, which uses data from emails sent by all Mailchimp users, A/B and Multivariate tests can tell you what your specific contacts like best.

Create multiple versions of your email that are identical in every way but the subject line, and we'll send them to randomly selected parts of your subscribed audience. We'll automatically send the email with the best open rate to the remainder of your subscribed audience, and you'll learn a little about what kind of subject line appeals to your contacts.

A/B testing is available to paid plans, and Multivariate testing is a Mailchimp Pro feature. To change your plan type, visit the plan page in your account.

Create an A/B Testing Campaign
Create a Multivariate Campaign