All glossary entries
Glossary
Bounce rate
The percentage of sent emails that came back undelivered. Above 5% is a deliverability emergency.
A bounce is an email that was rejected by the receiving server. Hard bounces (permanent — invalid address, domain doesn't exist) are different from soft bounces (temporary — mailbox full, server down). Mailbox providers care most about the hard bounce rate.
Industry-standard threshold: under 2% is healthy, 2–5% is concerning, over 5% triggers throttling at most providers. BoomSauce auto-pauses warmup on any mailbox that crosses 5% hard bounce rate.
High bounce rates are almost always a list-quality problem. Fix it at the source (better verification before upload, retire stale contacts) — not at the sending layer.
Related terms