An email bounce happens when the receiving server rejects a message. A hard bounce is permanent, for example an address that does not exist. A soft bounce is temporary, such as a full mailbox or a server outage. Bounce rate is bounced emails divided by emails sent, and a rising rate is an early warning of list problems.
What is the difference between hard and soft bounces?
Hard bounces come with permanent failure codes, usually 5xx in SMTP. Causes include a mistyped address, a deleted account or a domain that does not exist. Never retry these. Remove the address immediately.
Soft bounces usually carry 4xx codes. The mailbox may be full, the server may be down or the message may be too large. Sending platforms retry for a period, and after repeated soft bounces they usually treat the address as undeliverable.
How do you calculate bounce rate?
Divide bounced messages by messages sent and multiply by 100. For example, 50 bounces out of 5,000 sends is 1%. Some platforms measure against delivered plus bounced instead, so compare like with like when you switch tools.
There is no single official threshold. Many sending platforms warn or suspend accounts when hard bounces climb past a few percent, so check the policy of the provider you use. Treat any upward trend as a signal to investigate.
What causes high bounce rates?
- Purchased, scraped or very old lists.
- Typos at signup with no confirmation step.
- Role or throwaway addresses that were deleted.
- Misconfigured sending domain or blocked IP, which can produce policy bounces rather than address bounces.
- Messages that exceed size limits.
How do you reduce bounces?
- Use confirmed opt-in so every address is verified by its owner. See email list hygiene.
- Add basic validation on signup forms to catch obvious typos.
- Remove hard bounces after every campaign and suppress repeated soft bounces.
- Verify old or imported lists with a verification service before the first send.
- Read the bounce message text, because some bounces are blocks from your own reputation, not bad addresses. See blocklist removal.
How do bounces affect deliverability?
Providers read repeated sends to invalid addresses as sloppy list management, which lowers your reputation. See how reputation is scored. Keep bounces low as part of the habits in email deliverability best practices, and check the broader context in the deliverability overview.
Frequently asked questions
Is a soft bounce bad?
Occasional soft bounces are normal. Repeated soft bounces to the same address mean it is effectively undeliverable and should be suppressed.
What is a good bounce rate?
Lower is better. Many senders aim to stay around or below a couple of percent, but the real limit is set by your sending platform and mailbox providers, so check their policies.
Should I delete hard-bounced contacts?
Remove them from your sending list. Keep a suppression record so you do not import them again.
Does a bounce mean the address is gone forever?
A hard bounce means the failure is permanent. The person may have a new address, which you can ask for through another channel.