What is an email bounce back?

An email bounce back refers specifically to a notification indicating that an email delivery has failed. This typically occurs when the recipient's email address is invalid, their mailbox is full, or the email server is down temporarily. When a bounce back occurs, the sender receives an automatic notification from the email server highlighting the issue that caused the delivery to fail. This serves as an important feedback mechanism, allowing the sender to take appropriate action, such as correcting the email address or trying to resend the message later.

The other choices do not accurately define what an email bounce back is. A confirming message from the recipient indicates that an email has been received successfully, which is the opposite of a bounce back. A promotional message sent by email services describes marketing or advertisement communications rather than a delivery failure notification. Lastly, a request for sending emails in bulk usually pertains to mass email marketing efforts and does not relate to any failure or notification about an undelivered email. Therefore, the correct answer accurately captures the essence of what a bounce back entails in email communication.