Measuring the impact of email marketing involves analyzing various metrics: 1. Open Rate: The percentage of recipients who open the email. 2. Click-Through Rate (CTR): The percentage of recipients who click on links within the email. 3. Conversion Rate: The percentage of recipients who take the desired action after clicking on the email. 4. Bounce Rate: The percentage of emails that could not be delivered. 5. Unsubscribe Rate: The percentage of recipients who opt out of the email list after receiving the email.