Which of the following describes a Hard Bounce?

A hard bounce refers specifically to an email that cannot be delivered due to an invalid email address or a permanent reason associated with the recipient's mail server. This situation typically arises when the address does not exist, is incorrectly spelled, or is no longer in use. When a hard bounce occurs, the sending server typically acknowledges that the email cannot be successfully delivered and will not attempt to resend it.

In contrast, other classifications of email delivery failures, such as temporary issues or queued messages for later delivery, do not fall under the definition of a hard bounce. A message that is queued for later delivery may still be valid and can potentially be sent once the issues are resolved, while a soft bounce would indicate a temporary problem (e.g., a full mailbox) that might be resolved later. Thus, the definition provided aligns accurately with standard email delivery classifications.