Write subject lines people actually open with Mailchimp

A good subject line is short, specific, and gives the reader a reason to open. Aim for nine words or around 60 characters. Other things that make a good email subject line include:

• Personalize where you can: Using a subscriber's name or referencing their behavior consistently lifts open rates.
• Use emoji and punctuation sparingly: One emoji adds personality. Several in a row signal noise.
• Avoid spam trigger words: Certain phrases send your email straight to junk before anyone sees it. Catchy subject lines that drive opens are a solid reference when you're starting from scratch.

Mailchimp's subject line helper works automatically as you write inside the campaign builder. Green checkmarks confirm best practices; alerts flag issues with specific suggestions to fix them. You can also review recent subject line performance history in the tool to spot patterns over time. For a broader framework, subject line testing covers what separates high performers from low ones.

The subject line helper evaluates your subject line across five areas, powered by data from more than 10,000 emails sent per second through Mailchimp:

• Word and character count: It flags lines that are too long to display properly on mobile.
• Punctuation use: It catches overuse that reads as spammy to both readers and filters.
• Emoji use: It highlights when you've gone from expressive to excessive.
• Industry best practices: It checks your subject line against established patterns for your sending category.
• Spam risk: It surfaces problematic language before it causes a problem.

A subject line test sends two versions of the same email, each with a different subject line, to separate segments of your list. The version with the higher open rate wins and is automatically sent to the rest of your audience. It's the most reliable way to make decisions based on your actual subscribers rather than general data. Subject line tests are available on all paid Mailchimp plans. Explore AI-generated email subject lines if you want to generate variations faster.

Select Create → Email → A/B test, then choose the subject line as your variable. For formal email sends, nailing the right tone in your variations matters as much as the words themselves. From there:

• Write two variations: Keep everything else in the email identical so you're testing one thing at a time.
• Set the percentage of your list: It determines how many subscribers receive the test before the winner is chosen.
• Let Mailchimp send the winner: It goes automatically to your remaining contacts based on open rate.

The subject line helper gives you real-time feedback as you write. It catches length, punctuation, and spam issues before anything gets sent. A subject line test tells you what your specific audience responds to once it does. For example, last-chance email subject lines perform very differently across audiences — the kind of variation only a live test can reveal. Use the helper to write a stronger subject line. Use the test to find out which one wins.