A hard bounce is a permanent delivery failure — the email address doesn't exist or the domain is invalid — meaning that address should be removed from future sends. A soft bounce is a temporary delivery failure — a full inbox, a temporarily unavailable server — where a retry might succeed later.
Why it matters
Continuing to send to addresses generating hard bounces damages sender reputation and deliverability over time, which is why list hygiene practices typically involve automatically suppressing hard-bounced addresses, while soft bounces are usually retried rather than immediately removed.
In a sentence
"We automatically suppress any address after a single hard bounce, but allow up to three soft bounces before removing it from the active list."
Related terms
- Often confused with: Spam trap (Part One, Category 5) — a bounce is a delivery failure signal; a spam trap is a specific type of address that, if emailed, signals poor list hygiene to mailbox providers, regardless of whether the send technically bounced or not).