What defines a hard bounce?

A hard bounce is best defined as emails that are permanently undeliverable. This situation typically occurs when the recipient's email address is invalid or no longer exists, meaning that the server generates a return message indicating that it cannot deliver the email. Unlike soft bounces, which may occur due to temporary issues like a full inbox or server downtime, hard bounces signify a definitive issue with the email address itself.

Understanding hard bounces is crucial for maintaining a clean email list, as repeatedly sending emails to invalid addresses can harm the sender's reputation and potentially lead to being flagged as spam. By identifying and addressing hard bounces, marketers can improve the effectiveness of their campaigns and ensure better delivery rates in the future.