Free email bounce rate calculator.
Two numbers in, one verdict out: your bounce rate measured against the thresholds inbox providers actually act on. The reference below covers what each SMTP failure code is telling you, because the code decides whether this is a list problem or a reputation problem.
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Bounce rate at a glance
| Item | Value |
|---|---|
| The calculation | Bounces divided by messages sent, as a percentage |
| The line | 2%. Past it, providers start reading your sending as guesswork |
| A verified list | Runs close to zero, which is the standard rather than the threshold |
| Hard versus soft | A 5.x.x code is permanent, a 4.x.x code is temporary. Reputation damage comes from the first |
| Data decay | Roughly 2 to 3% of B2B addresses go stale every month, without notifying anyone |
What is email bounce rate?
Bounce rate is the share of messages a receiving server refused rather than delivered, expressed as a percentage of what you sent. It is the one metric inbox providers treat as a confession.
The reasoning is unflattering but fair. Engagement can be argued with: people are busy, subject lines vary, timing matters. A hard bounce cannot be argued with. It means you sent mail to an address that does not exist, and a sender who does that at volume is a sender who did not check. Providers respond by applying more scepticism to everything else you send, including the campaigns that were working.
Which makes bounce rate a leading indicator rather than a result. By the time placement drops, the bounces that caused it happened days ago.
How to read your result
The calculator returns your rate, a verdict against the thresholds, and the fixes that match where you landed.
Below the line comes back with the maintenance advice rather than congratulations: re-verify anything older than about thirty days, because B2B data decays continuously through job changes and acquisitions.
Above the line comes back with three fixes in priority order: verify the whole list before the next send, confirm the domains you are mailing actually accept mail, and, if bounces spiked suddenly on a list that was already verified, look at your sending reputation rather than your data.
That third one is the distinction the rest of this page exists to explain. A rising bounce rate on a clean list is usually not a list problem at all, and re-verifying will not fix it. The failure codes tell you which situation you are in.
What each bounce code means
Enhanced status codes follow RFC 3463. The first digit is the one that matters: 4 means temporary, 5 means permanent.
| Code | Class | What it means | What to do |
|---|---|---|---|
5.1.1 | Hard | No such mailbox at that domain. | Remove immediately. This is the classic reputation-damaging bounce. |
5.1.2 | Hard | The domain itself does not exist or accepts no mail. | Remove, and look at where that data came from. |
5.2.1 | Hard | Mailbox disabled or suspended. | Remove. Usually someone who left. |
5.7.1 | Hard | Refused on policy grounds: authentication, reputation or a block rule. | Not a list problem. Check SPF, DKIM, DMARC and your sending reputation. |
4.2.2 | Soft | Mailbox full. | Retry. Remove only after it repeats across several sends. |
4.3.2 | Soft | System not accepting messages right now, often greylisting. | Nothing. Retries handle it automatically. |
4.4.1 | Soft | No answer from the receiving host. | Retry. |
4.7.x | Soft | Rate limited by the receiver. | Slow down. This is a volume signal, and ignoring it escalates to a block. |
What your rate is telling you
| Rate | What it means | What to do |
|---|---|---|
| Under 1% | A properly verified list. | Keep verifying. Re-check anything over a quarter old. |
| 1 to 2% | Acceptable, and drifting. Usually ageing data. | Re-verify the oldest segments before the next campaign. |
| 2 to 5% | Providers are now reading your sending as guesswork. | Pause, re-verify everything, resume at lower volume. |
| Over 5% | Reputation damage in progress, on every domain sending that list. | Stop today. Every further send compounds it. |
How to recover from a bounce spike
- Pause the campaign, not just the segment. Every additional send while the rate is high adds to the damage.
- Read the codes before the data. If most failures are 5.7.1, this is a reputation or authentication problem and re-verifying the list will change nothing.
- Trace the segment back to its source. Scraped, bought, permutated without verification, or simply old. The answer determines whether the rest of that source is safe.
- Re-verify everything, not only the part that bounced. The bounces you saw are a sample of the problem, not its boundary.
- Resume at reduced volume. Come back at roughly half and step up over a week while watching placement.
- Put re-verification on a schedule. Quarterly at minimum, and always before a campaign that puts real volume behind an older segment.
Common questions about bounce rate
What is the difference between a hard and a soft bounce?
Hard is permanent: the address does not exist. Soft is temporary: mailbox full, server busy, greylisting. Reputation damage comes overwhelmingly from hard bounces, because a hard bounce says you mailed somewhere you had no reason to believe was real.
Why is 2% the line?
It is roughly where major providers stop reading your sending as informed and start reading it as guesswork. Below it, a bad address is noise. Above it, everything else you send gets more scepticism, including the campaigns that were working fine.
My bounce rate spiked on one campaign. What should I do?
Pause it. A spike is a list problem, and every further send compounds it. Re-verify the segment, work out where it came from, scraped, stale or permutated without verification, and leave it paused until the source is fixed rather than the symptom.
Does a very low bounce rate improve deliverability?
It removes a reason to filter you. Near-zero bounces are table stakes rather than an advantage: it is simply what a sender who knows their list looks like. The actual advantage comes from engagement, and engagement comes from the message.
What does a 5.7.1 bounce mean if my list is verified?
That it is not a list problem. 5.7.1 is a refusal on policy grounds, which usually means authentication is failing or your sending reputation has dropped far enough for the receiver to block outright. Check SPF, DKIM and DMARC first, then recent volume against your warmup schedule.
Do soft bounces count against me?
Barely, on their own. A full mailbox or a busy server says nothing about how you built your list, and retries usually resolve it. What does count is ignoring a rate-limit response and continuing at the same volume, because that turns a temporary refusal into a durable block.
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