A message that doesn’t get delivered promptly is said to have bounced. Emails can bounce for more than 30 reasons: the email address is incorrect or has been closed; the recipient’s mailbox is full, the mail server is down, or the system detects spam or offensive content. See hard bounce and soft bounce.

Building a Highly-targeted Opt in List: When Money Lies Beneath the Lists
Are you successful with your Internet business? Better yet, do you think you are successful with your online business? When most online entrepreneurs are asked with these questions, they often brush it off.