What Is Email Bounce Rate?
The percentage of sent emails that are returned by the recipient's mail server, either permanently (hard bounce) or temporarily (soft bounce).
Email bounce rate is the percentage of sent emails that are returned (bounced) by the recipient's mail server and not delivered. Bounce rate is one of the most important deliverability metrics for cold email — high bounce rates signal to receiving mail servers that your list quality is poor, which damages your domain's sender reputation and worsens deliverability for future campaigns.
Hard bounce vs. soft bounce
- Hard bounce: Permanent delivery failure. The email address does not exist, the domain does not exist, or the receiving server has permanently rejected the sender. Hard-bounced addresses should be immediately added to your suppression list and never emailed again.
- Soft bounce: Temporary delivery failure. The recipient's mailbox is full, the mail server is temporarily unavailable, or the email was too large. Soft bounces may resolve on retry, but an address that soft-bounces repeatedly should be treated as a hard bounce.
Acceptable bounce rate thresholds
- Under 2%: Acceptable for cold email — your list quality is reasonable
- 2–5%: Concerning — review list sources and consider additional email verification
- Above 5%: Dangerous — your sending reputation is at risk; pause and clean the list before continuing
- Above 10%: Critical — your domain reputation is being damaged; stop sending and address the root cause immediately
How to keep bounce rate low
- MX-validate every email address before adding to a campaign (confirms the domain has active mail exchange records)
- Never guess or construct email format patterns — guessed addresses produce high bounce rates
- Use only first-party, verified contact sources
- Regularly clean stale lists — contacts older than 12–18 months should be re-verified
Related terms
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