What is bounce rate?

Bounce rate measures the percentage of emails that could not be delivered and were returned by the receiving server. A bounce is the mailbox provider telling you the message did not make it to the mailbox. Behind the scenes, each failed attempt includes an SMTP status code explaining why the delivery could not continue.

It is one of the most important health indicators in email. High bounce rates signal poor list hygiene, domain issues, or problems with data collection.