What is a good bounce rate for cold email?

As close to zero as verification allows. Gmail and Yahoo publish no bounce threshold, but repeated hard bounces hurt reputation, so a rate that climbs from one campaign to the next is a sign your list was not verified.

Should I retry a soft bounce?

Yes, a few times over a day or two. If the same address keeps soft bouncing over several sends, treat it like a hard bounce and remove it.

Is bounce rate the same as website bounce rate?

No. Website bounce rate is the share of visits that leave after one page. Email bounce rate is about messages that could not be delivered.

Bounce rate: what it means for email

The formula

Bounce rate = bounced messages / sent messages x 100

Use sent, not delivered, as the denominator, and count each recipient once per campaign. Track hard and soft bounces separately as well as together, because they mean different things.

Hard bounce versus soft bounce

Mail servers reply with three-digit codes defined in RFC 5321. A code starting with 5 is a permanent failure. A code starting with 4 is a temporary one.

Type	SMTP code family	Common causes	What to do
Hard bounce	5xx (for example 550)	Mailbox does not exist, domain does not exist, address blocked	Remove immediately, never retry
Soft bounce	4xx (for example 421, 452)	Inbox full, server busy, message temporarily deferred	Retry; remove if it persists

One grey area: some providers return a 5xx code for a policy rejection (your message looked like spam) rather than a missing mailbox. That is a reputation problem, not a list problem, and removing the address will not fix it.

A worked example

You send a first email to 800 people. 24 come back with 550 "user unknown" and 8 come back with 452 "mailbox full".

Hard bounce rate: 24 / 800 = 3.0%
Soft bounce rate: 8 / 800 = 1.0%
Total bounce rate: 32 / 800 = 4.0%

The 3% hard bounce rate says the list was not verified well enough. Remove the 24, retry the 8 tomorrow, and run email verification on everything before the next send.

Why bounces matter

Mailbox providers read a sender who often hits non-existent addresses as one who bought or scraped a list. Repeated hard bounces hurt your sender reputation, and reputation decides whether your other emails reach the inbox. That is the core of email deliverability.

Data quality varies widely. Third-party reviews report bounce rates of 15% to 35% on Apollo's data, and Apollo itself refunds a verified email that bounces within 30 days. Refund policies like that exist because no database is perfectly current.

Common mistakes

Retrying hard bounces. It only adds more failures to your record.
Ignoring [catch-all email](/glossary/catch-all-email) domains. They pass verification and bounce later, which surprises people.
Only measuring the whole account. Break bounce rate down by list source; one bad source can hide inside a decent average.

Our article on cold email bounce rate covers how to bring a high rate down.

How Sluice handles bounces

Sluice verifies every address before billing it, refunds a bounce exactly what it cost, once, and stops any email sequence for that person. Insights shows bounce rate by source, so you can see which source is sending you bad addresses.