# What is hard bounce? Definition and examples · Leadraft

URL: https://leadraft.co/glossary/hard-bounce
Summary: A hard bounce is a permanent delivery failure, such as an address that doesn't exist, returned with an SMTP reply code starting with 5.

Glossary · Email & deliverability · Last updated October 31, 2026

# Hard bounce

A hard bounce is a permanent delivery failure, such as an address that doesn't exist, returned with an SMTP reply code starting with 5.

**Also called:** Permanent bounce, Permanent failure.

Under RFC 5321, reply codes starting with 5 mean permanent failure. The most common hard bounce is `550 5.1.1`, where the enhanced status code `5.1.1` (RFC 3463) means "bad destination mailbox address": no such user. Other hard bounces include domains that don't exist or accept no mail.

A hard bounce means stop. Microsoft's Outlook.com policy says that after a permanent failure the sender must not try to retransmit that message to that recipient, and Amazon SES bases its bounce rate on hard bounces. Every hard bounce should go straight onto your suppression list so no future campaign, client or export sends to it again.

Not every `5xx` reply is about the address. Codes in the `5.7.x` range are usually policy rejections of the sender, such as failed authentication. Outlook, for example, rejects non-compliant high-volume mail with `550 5.7.515`. Those look like hard bounces in a dashboard but point to your setup, not your list.

For local business lists, hard bounces mostly come from guessed addresses, former staff mailboxes and closed businesses. Verifying shortly before sending removes most of them.

## Example

An email to `jsmith@acmedental.com` comes back with `550 5.1.1 The email account that you tried to reach does not exist`. The address is suppressed permanently.

## Sources

1.  1.[IETF, RFC 5321: Simple Mail Transfer Protocol](https://www.rfc-editor.org/rfc/rfc5321)
2.  2.[IETF, RFC 3463: Enhanced Mail System Status Codes](https://www.rfc-editor.org/rfc/rfc3463)
3.  3.[Microsoft, Outlook.com Postmaster policies](https://substrate.office.com/ip-domain-management-snds/postmaster/Policies)
4.  4.[Amazon SES, Reputation metrics messages (bounce, complaint and spamtrap notices)](https://docs.aws.amazon.com/ses/latest/dg/reputationdashboardmessages.html)

## Related terms

-   [Soft bounceA soft bounce is a temporary delivery failure, such as a full mailbox or busy server, returned with an SMTP reply code starting with 4.](https://leadraft.co/glossary/soft-bounce)
-   [Bounce rateBounce rate is the percentage of sent emails that were returned as undeliverable; for cold email, under 2% is a sensible target.](https://leadraft.co/glossary/bounce-rate)
-   [Suppression listA suppression list is a list of addresses or domains you must never email again, such as opt-outs, hard bounces and complaints, checked before every send.](https://leadraft.co/glossary/suppression-list)
-   [SMTPSMTP (Simple Mail Transfer Protocol) is the standard, defined in RFC 5321, that mail servers use to send and relay email to each other.](https://leadraft.co/glossary/smtp)

## Further reading

-   [What's a good cold email bounce rate?](https://leadraft.co/blog/cold-email-bounce-rate)
-   [How email verification works](https://leadraft.co/blog/how-email-verification-works)

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Last built: 2026-11-09