Email Bounce Rate
By Federico Donatone · Updated October 15, 2026Email bounce rate is the percentage of sent emails that are returned as undeliverable instead of reaching a mailbox. A hard bounce means the address does not exist or the domain cannot receive mail. A soft bounce is a temporary failure, such as a full inbox. High bounce rates damage the sender's domain reputation.
How to calculate email bounce rate
Email bounce rate = Bounced emails ÷ Emails sent × 100If you send 1,000 emails and 15 come back as undeliverable, your bounce rate is 15 ÷ 1,000 × 100 = 1.5%.Track hard and soft bounces separately, and break both down by mailbox and by list source. A single blended number hides the list that is doing the damage. Count first emails and follow-ups together, because a bounce on step three hurts the domain as much as one on step one.
Hard bounce vs soft bounce
| Hard bounce | Soft bounce | |
|---|---|---|
| What it means | Permanent failure | Temporary failure |
| Common causes | Address does not exist, domain has no mail server | Full inbox, busy server, message too large |
| What to do | Remove the address at once, never retry | Retry later, remove it if it keeps failing |
| Effect on reputation | Strong negative signal | Weaker, unless it repeats |
Hard bounces are the ones that hurt. Each one tells the receiving provider that you are mailing addresses you never checked, which is exactly the pattern spam filters look for.
Soft bounces deserve attention when they cluster. A run of temporary failures from one mailbox provider in a short period can mean that provider is slowing down or refusing your mail, which is a reputation problem rather than a list problem.
What causes a high bounce rate in cold email
In outbound, the first place to look is the contact data: addresses a data provider labeled valid that do not exist. To measure it, we ran the same 600 leads through 8 contact data providers and verified every email. Every provider shipped some dead emails inside its valid label (Growth Cab test of 8 contact data providers):
| Provider | Dead emails labeled valid |
|---|---|
| RocketReach | 63 |
| Lusha | 49 |
| Apollo | 24 |
| Seamless.AI | 4 |
| LeadMagic, Hunter, Icypeas | 3 each |
| Prospeo | 1 |
Each of those addresses would have gone out as a likely hard bounce. The full method and coverage numbers are in our lead generation database benchmark. The lesson: a valid label is a vendor claim until an outside verifier agrees.
Other causes are worth checking too: old lists whose contacts have changed jobs, guessed addresses built from a name pattern, typos from manual entry, and company domains that stopped receiving mail after an acquisition or a rebrand.
How to reduce email bounce rate
- Verify every address with an outside verifier before it enters a sequence, even when the provider says valid.
- Keep catch-all and guessed addresses out of the first send.
- Remove contacts at domains with no MX record, since those domains usually cannot receive email.
- Suppress every hard bounce immediately and never retry it.
- Retest a sample from your data provider every quarter, because contact data goes stale as people change jobs.
The free GTM diagnostic skills for Claude on our free tools page include a lead list QA skill that flags duplicates, invalid and role emails and domains with no mail server, plus our free cold email domain checker for your sending setup. If bounces stay high after verification, an email deliverability consultant can read the bounce codes to find the cause.