Double Opt-In: Use a double opt-in process to confirm email addresses. This involves sending a confirmation email to the user after they sign up, ensuring that the email address is valid. Data Cleaning: Regularly clean your email list by removing inactive or invalid email addresses. This can be done manually or using email validation tools. Email Verification Services: Use third-party email verification services to check the validity of email addresses in your list. These services can identify and remove invalid addresses. Segmentation: Segment your email list based on engagement levels. Regularly monitor and remove unengaged subscribers to maintain a high-quality list.