- Double Opt-In: Requires users to confirm their email address by clicking on a verification link sent to their inbox. - Email Verification Services: Use third-party tools and services to clean and verify your email list. Examples include ZeroBounce, NeverBounce, and BriteVerify. - Real-Time Verification: Integrates verification into your sign-up forms to instantly check the validity of an email address as users enter it. - Manual Verification: Manually check and validate email addresses, though this is time-consuming and less efficient.