What is bounce rate?
Bounce rate is the share of sent messages that were returned as undeliverable, shown as a percentage: bounces divided by messages sent. Hard bounces count against reputation far more heavily than soft bounces, and sending platforms can pause accounts whose bounce rate exceeds their limits.
Mailbox providers do not publish a single bounce threshold. Sending platforms do set their own, and they enforce them by warning, throttling or suspending accounts. Check the limit for the platform you send through.
Hard and soft bounces are not equal. A full mailbox resolves itself; an address that does not exist never will, and repeatedly sending to it is the specific behaviour that damages reputation.
Bounce rate is predictable before a send. Verifying the list tells you roughly the rate you would have had, which turns a reputation problem into a filtering step.
Example
How SimpleVerifier handles it
After a list is verified you get separate valid, risky and invalid files. Sending only the valid file removes the addresses that would hard bounce.
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By SimpleVerifier Team · Last reviewed 2026-10-13 · All 50 glossary terms