E-mail message that is undeliverable because of an erroneous address or other permanent cause.

This is when an email is returned undelivered because the recepient or host is unknown, or the sender has been blocked by the recepient's ISP or Mail Server.

A hard bounce is an e-mail message that has been returned to the sender because the recipient's address is invalid. A hard bounce might occur because the domain name doesn't exist or because the recipient is unknown. When the recipient's name is known, e-mail may be rejected because the sender's mail box is full or for other reasons. This is known as a soft bounce.

a message that's permanently undeliverable because the address is non-existent or invalid, or because the recipient's mail server is blocking your mail server

an email address that is undeliverable because of permanent failure, such as "This account does not exist

an email message that has been returned to the sender and is permanently undeliverable

an e-mail message that has been returned to the sender because the recipient's address is not valid

an undeliverable message which is probably due to a permanent problem with the address

a permanent error, meaning the email address is no longer valid

a permanently failed address

a "user unknown" or "host unknown" error message when delivery is attempted

An email message which is returned with as being permanently undeliverable. An example of a hard bounce would be a message which is returned because the recipient's email address does not exist. See also "Soft Bounce".

A message that can't be delivered because the address is invalid (the account does not exist or it has been abandoned by the user).

A hard bounce is the failed delivery of an email due to a permanent reason, such as a non-existent email address. (Also see Soft Bounce)

An email message that permanently fails to reach its intended recipient but instead returns to the sender. Causes include non-existent domains and the recipient being unknown.

Message sent to an invalid, closed or nonexistent email account.

Message sent to an invalid, closed or nonexistent e-mail account.

A Hard Bounce happens when the email address is no longer valid.

When an email message you have sent is returned to you without reaching the recipient. Often it will be returned with the message "user unknown" or "host unknown." A hard bounce occurs most often because of an error in a subscriber's email address (misspelled, wrong host). You should unsubscribe hard bounces from your list.

Bounced e-mail that could never get through because the e-mail address doesn't exist or the domain doesn't exist.

An e-mail that has bounced back to the sender undelivered.