Bounce Rate
The percentage of emails that could not be delivered to the recipient's inbox.
Bounce rate is calculated as (bounced emails / total sent emails) × 100. There are two types of bounces:
Hard bounces occur when an email is permanently undeliverable — the mailbox doesn't exist, the domain is invalid, or the server has explicitly rejected the message. Hard bounces should be immediately removed from your list.
Soft bounces are temporary delivery failures — the mailbox is full, the server is down, or the message is too large. Soft bounces may succeed on retry, but persistent soft bounces (3+ attempts) should be treated as hard bounces.
Industry benchmarks:
- Under 2%: Good — your list is healthy
- 2-5%: Warning — you need to clean your list
- Over 5%: Critical — risk of blacklisting and sender reputation damage
ISPs like Gmail and Microsoft closely monitor bounce rates. A bounce rate above 5% can trigger spam filtering or outright blocking of your sending domain.
Related Terms
Hard Bounce
A permanent email delivery failure caused by an invalid address, non-existent domain, or server rejection.
Soft Bounce
A temporary email delivery failure that may succeed on retry.
Sender Reputation
A score assigned by ISPs to your email sending domain/IP that determines whether your emails reach the inbox.
Email Verification
The process of confirming whether an email address is valid, deliverable, and belongs to a real person.
Related Blog Posts
Want to learn more?
Read our in-depth blog posts on email verification and deliverability.