The Subject Line Optimizer analyzes your historical email performance using True Open data to help you evaluate and refine your subject lines before sending.
By comparing your current subject line against patterns from your highest- and lowest-performing emails, the optimizer provides data-informed insights to support your final decision.
Quick Reference
- The Subject Line Optimizer is available in the Review and Send stage of the new Email Composer.
- It uses True Open data to reduce the impact of bot and security-related activity.
- An administrator must enable the feature under Settings > Custom Account Settings > Labs.
- At least 10 emails sent within the past year (to 100+ recipients each) are required.
- Recommendations are informational and do not guarantee results.
Admin opt-in required: An Act-On administrator must enable the Subject Line Optimizer in Settings > Custom Account Settings > Labs.
Email history required: At least 10 email messages sent within the past year, each to 100 or more recipients, are required for the optimizer to generate recommendations.
How the Subject Line Optimizer Works
Performance Analysis
The optimizer reviews historical email performance to identify patterns linked to stronger and weaker open rates. It evaluates characteristics such as subject line length, wording, and structure using True Open data to exclude non-human activity.
Your current subject line is then compared against these patterns to highlight elements that align with past success or may be associated with lower engagement.
Personalized Recommendations
Based on your account’s email history, the optimizer presents tailored insights that show how closely your subject line matches historical performance trends.
These insights are designed to inform - not replace - your judgment when finalizing a subject line.
Using the Subject Line Optimizer
Use the Subject Line Optimizer as part of your standard email review and send process.
- Create or edit an email using the new Email Composer.
- Navigate to the Review and Send page.
- Locate the Subject Line Optimizer in the subject line section.
- Click Start analysis to generate recommendations.
- Review the insights and apply any changes you choose.
Keep in Mind
- Run the optimizer after completing your email content to ensure the analysis reflects the final message.
- Recommendations are based on historical trends and do not guarantee future performance. Always apply your own judgment before sending.
Admin Setup
To enable the Subject Line Optimizer:
- Go to Settings.
- Select Custom Account Settings.
- Open the Labs tab.
- Enable the Subject Line Optimizer feature.
For additional guidance, see related articles on reviewing and sending email, or contact your Act-On administrator or support team.