The primary metrics for A/B testing subject lines include:
Open Rate: The percentage of recipients who open your email. This is often the most critical metric for subject line testing. Click-Through Rate (CTR): The percentage of recipients who click on links within the email. This helps gauge the effectiveness of the subject line in driving engagement. Conversion Rate: The percentage of recipients who complete a desired action, such as making a purchase or filling out a form. Bounce Rate: The percentage of emails that were not delivered. While this is more related to your email list quality, it can indirectly affect your results.