Hard Bounce

A hard bounce is a failed email delivery caused by a permanent problem, such as an invalid email address, a domain that does not exist, or an address that cannot receive mail. When an email hard bounces, you should stop sending to that address.

Hard bounces matter because mailbox providers treat repeated sends to bad addresses as a sign of poor list quality. Too many hard bounces can damage sender reputation and make future email more likely to land in spam.

Hard bounce vs soft bounce

A hard bounce says the destination is not valid or cannot receive the message. A soft bounce says delivery failed for now, but the address may still be valid.

Common causes of hard bounces

Invalid email address. The user mistyped the address, used a fake address, or signed up with an address that does not exist.

Dead domain. The domain no longer exists or does not accept email.

Removed mailbox. The person left a company, deleted an account, or lost access to that mailbox.

Blocked recipient address. The receiving system permanently rejects mail for that address.

Imported stale contacts. Old lists often contain addresses that were valid years ago but are no longer active.

How to handle hard bounces

Suppress immediately. Do not keep retrying an address that hard bounced. Continuing to send wastes volume and harms reputation.

Keep a suppression list. Store the address so future campaigns, workflows, and imports do not accidentally add it back.

Clean imports before sending. If you import old contacts, expect more bounces. Start with engaged contacts and avoid sending a full blast to stale addresses.

Watch bounce rate by source. If one form, integration, or campaign creates many hard bounces, fix the source of bad addresses.

Use confirmation where appropriate. For high-risk signup forms, verification emails or double opt-in can catch typos before they enter your list.

Separate account-critical handling. If a customer's billing or login email hard bounces, create an account-support workflow instead of silently dropping the issue.

Examples

Signup typo

[email protected] hard bounces because the user mistyped [email protected].

Expired company address

[email protected] hard bounces after the domain stops receiving mail.

Deleted mailbox

a former employee's address hard bounces after IT removes the mailbox.

Imported stale list

a three-year-old event list produces a spike in hard bounces because many contacts changed jobs.

How hard bounces affect deliverability

Mailbox providers use bounce behavior as one signal of sender quality. A healthy sender removes bad addresses quickly. A poor sender keeps mailing invalid contacts.

For SaaS teams, this matters across marketing and transactional email. A bad imported marketing list can hurt the reputation used by product-triggered email if sending domains and practices are not managed carefully. Keep list hygiene tight before volume grows.

Loops helps by managing bounce and suppression behavior as part of the sending system. Related reading: email deliverability, soft bounce, transactional emails, and email API.

FAQ

What is a hard bounce?
A hard bounce is a failed email delivery caused by a permanent issue, such as an invalid address, deleted mailbox, or domain that does not accept email.

Should I resend to a hard bounce?
No. Suppress the address after a hard bounce so future campaigns and workflows do not send to it again.

What causes hard bounces?
Common causes include typos, fake addresses, deleted mailboxes, dead domains, blocked recipient addresses, and old imported contacts.

How is a hard bounce different from a soft bounce?
A hard bounce is permanent and should be suppressed. A soft bounce is temporary, such as a full inbox or temporary server issue, and may resolve later.

Do hard bounces hurt deliverability?
Yes. High hard-bounce rates signal poor list quality and can damage sender reputation over time.

How can I reduce hard bounces?
Use clean signup forms, verify important addresses, avoid purchased or stale lists, suppress hard bounces immediately, and monitor bounce rate by source.