The percentage of sent emails that could not be delivered and were returned by the receiving server.
Bounce rate is the share of your sent messages that failed to deliver, expressed as a percentage. It combines hard bounces (permanent failures) and soft bounces (temporary ones), though hard bounces are what damage your standing.
A healthy hard-bounce rate is generally under 2%. Cross that line and mailbox providers begin to question your list quality — sustained high bounce rates throttle delivery and push even legitimate mail to spam. Some email platforms will suspend accounts that bounce too heavily.
Bounce rate is a lagging indicator: by the time you see it, the damage to your reputation is already done. Verifying addresses before you send keeps it low by design.
A permanent delivery failure that happens when an email is sent to an address that does not exist or cannot receive mail.
A temporary delivery failure caused by a transient issue, such as a full mailbox or a server that is briefly unavailable.
A trust score that mailbox providers assign to your sending IP and domain, which determines whether your mail reaches the inbox.
The ongoing practice of keeping an email list free of invalid, risky, and unengaged addresses.
See it in action
Check any address against BounceShift's multi-layer engine — syntax, MX, disposable, and role checks free, with full SMTP verification on signup.