Bounce rate is the percentage of sent emails that fail to deliver. Mail providers (and services like Amazon SES) actively watch this metric, since a high bounce rate is one of the strongest spam signals.
Reasonable thresholds
- Under 2%: healthy
- 2–5%: worth investigating list quality
- Above 5%: many providers (including AWS SES) will restrict or suspend sending at this point
Hard vs. soft bounces
A hard bounce means the address is permanently invalid (should be removed from your list immediately); a soft bounce is temporary (mailbox full, server briefly down) and can be retried, but repeated soft bounces to the same address should eventually be treated as a hard bounce.
FAQ
Should I keep emailing an address after it hard bounces?
No — continuing to send to hard-bounced addresses directly damages sender reputation and should be suppressed immediately, not just eventually cleaned up.