What is Bounce rate?
Bounce rate is the share of sent emails that were returned as undeliverable, usually reported as bounces divided by emails sent.
Also called: email bounce rate.
Bounces come in two kinds. A hard bounce is permanent: the address or domain does not exist. A soft bounce is temporary: a full mailbox, a server that is down, or a message that is too large. Most sending tools report both, and most deliverability advice is about the hard ones.
Bounce rate matters beyond the wasted lead. Mailbox providers read a high bounce rate as a sign the sender did not get permission or did not maintain the list, and it weighs on sender reputation, which decides whether the rest of your mail reaches the inbox.
There is no single official threshold for cold email. One 2026 benchmark report advises keeping bounces under 2%, ideally much lower, and the cold email calculator uses 2% as its default. If a test batch bounces far above that, stop and re-check the list before sending the rest.
The lever you control is the list: verify addresses before every campaign, send to catch-all addresses separately, remove anything that bounced, and re-verify lists that are more than a few weeks old.
In our data: Of the business emails in the 67Leads warehouse, the mail server refused 2% (728 of 44,205): those are the addresses that would hard-bounce, and they are never sold as verified.
Live from the 67Leads warehouse, 5 Nov 2026. Methodology.