Bounce rate

Bounce rate is the share of sent messages the receiving server refuses. A hard bounce means the address is permanently invalid; a soft bounce means a temporary problem such as a full mailbox or a throttled connection. Providers read a high hard-bounce rate as a sign you are mailing a list you did not collect yourself, so suppress hard bounces immediately and keep the rate well under one per cent. Persistent soft bounces should eventually be suppressed too.