An email that could not be delivered and came back. A hard bounce is permanent, such as an address that does not exist. A soft bounce is temporary, such as a full mailbox or a server that is briefly down.
Formula
Bounce rate (email) = bounced emails ÷ emails sent × 100
Example
Meera sends to 8,200 addresses and 200 bounce, so 8,000 are delivered. Her tool stops sending to the hard bounces at once and retries the soft ones on later sends.
How you'll hear it
“Clean out the hard bounces before Diwali; they're dragging down our sender reputation.”
Don't confuse it with
- Bounce rate (website): visitors who left after one page, an analytics term with the same word.
- Unsubscribe: the person chose to leave; a bounce is a delivery failure.
Related terms
Sources
- Soft vs. Hard Bounces, Mailchimp (Intuit)
- Email analytics: 13 email marketing metrics you should track, HubSpot, 2026