What is an Email Bounce?
An email bounce occurs when an email message cannot be delivered to the recipient and is returned to the sender. The bounce message (also called a Non-Delivery Report or NDR) contains an error code explaining why delivery failed.
Hard Bounce vs Soft Bounce
| Hard Bounce | Soft Bounce |
|---|---|
| Permanent delivery failure | Temporary delivery failure |
| Address doesn't exist, domain invalid | Mailbox full, server temporarily down |
| Remove immediately from list | Retry delivery, remove after repeated failures |
| Severely damages sender reputation | Minor impact unless persistent |
Acceptable Bounce Rates
Industry best practice is to keep your hard bounce rate below 2%. Most ESPs (Mailchimp, SendGrid, etc.) will suspend your account if your bounce rate exceeds 5%. Regularly validating your email list is the most effective way to prevent bounces.
Preventing Bounces
- Validate emails at point of collection (signup forms, checkout).
- Run bulk validation on existing lists before campaigns.
- Remove hard bounces immediately and permanently.
- Use double opt-in to confirm email ownership.
Prevent bounces before they happen. Validate your email list with Mailchk's bulk validation or real-time API.