We’ve launched a new AI-powered Subject Line Optimizer. This feature analyzes your own historical email performance (using True Open data) to assess a draft subject line and generate up to four data-driven alternatives. You can access it directly from the Review & Send page when creating an email message.
When
The Subject Line Optimizer will be available to all accounts in North America starting October 2, 2025. It is not currently available for accounts outside North America.
Customer Impact
The optimizer is available as an opt-in Labs feature. Administrators can activate it in Settings > Custom Account Settings > Labs.
This tool helps improve campaign engagement by providing subject line recommendations based on your own performance history. For setup instructions and usage details, see our Subject Line Optimizer support article.