Hard Bounce
A hard bounce is an email that the receiving server permanently rejects, typically because the address is invalid, mistyped, the domain doesn't exist, or the mailbox has been closed. Unlike a temporary failure, a hard bounce will never succeed on retry, so the address should be removed from your list right away.
Email platforms usually suppress hard-bounced addresses automatically to protect your sender reputation, since mailbox providers treat repeated sends to dead addresses as a sign of a poorly maintained list. The hard bounce rate is the share of sent emails that hard bounce; keeping it low signals a clean, well-sourced list.
The main pitfall is mailing old or purchased lists, which produces spikes of hard bounces that can hurt deliverability for everyone on the list. Contrast this with a soft bounce, which is temporary. Related terms include email deliverability and double opt-in.
Last updated: 14 June 2026