Email Bounce Rate
The share of sends that come back undeliverable.
Stay under 2% — above 5% risks your sender reputation.
Definition
Email bounce rate is the percentage of sent messages that are returned undeliverable, counting both hard bounces (permanent failures) and soft bounces (temporary failures) divided by total sends. A rate above roughly 2% invites throttling from mailbox providers, and above 5% risks serious, lasting damage to sender reputation.
We verify millions of addresses before they ever reach a send queue, and bounce rate is the single number that tells senders whether that queue is healthy. It is not just a vanity metric buried in a campaign report. Mailbox providers watch it closely, weight it heavily in reputation scoring, and act on it fast, so understanding what drives the number, and how to keep it down, matters to anyone who sends email at volume.
Hard bounces vs soft bounces
Bounce rate combines two very different failure types, and the mix matters as much as the total. A hard bounce is permanent: the mailbox does not exist, the domain is invalid, or the receiving server refuses the address outright with a 5xx response. No amount of retrying fixes a hard bounce, and a high hard-bounce share is the strongest signal to providers that a list was never properly maintained.
A soft bounce is temporary: a full inbox, a server that is briefly down or overloaded, or a message that is too large, all delivered as a 4xx response. Sending servers typically retry a soft bounce automatically for a day or two, and many resolve on their own. Both types count toward the combined bounce rate, but providers weigh them differently, since a high soft-bounce share often points to a transient issue rather than a list-quality problem.
The thresholds that matter
Bounce rate is calculated as (hard bounces + soft bounces) / total sent × 100, and most email service providers report it automatically per campaign. The number on its own means little without the thresholds providers use to judge it.
- Under 2%. Generally considered healthy, and the level most mailbox providers expect from a well-maintained, permission-based list.
- 2% to 5%. A warning zone. Deliverability starts to soften here, and providers may begin throttling volume or routing more mail to spam.
- Above 5%. Treated as a real list-hygiene problem. Sustained rates in this range can trigger sending blocks and sender-reputation damage that outlasts the campaign that caused it.
Because reputation is cumulative and shared across a sending domain or IP, a single high-bounce send can depress deliverability for every campaign that follows, well after the offending list has been cleaned up.
What drives a high bounce rate
The most common cause is ordinary list decay. Roughly 20-30% of email addresses go stale every year as people change jobs, switch providers, or abandon accounts, so a list that is never re-verified ages steadily into a bounce problem, even if it was clean the day it was collected. Typos at signup add a steady trickle of invalid addresses from day one, since a single mistyped character turns a real inbox into a hard bounce.
Purchased or scraped lists are the riskiest source by far. These addresses were often never opted in, may already be stale by the time they are bought, and are disproportionately likely to include spam traps and disposable addresses, both of which surface as bounces or complaints rather than clean sends. A single campaign against a purchased list can push bounce rate well past the danger threshold on its own.
How pre-send verification keeps bounce rate near zero
The most reliable way to control bounce rate is to stop bad addresses before they leave the queue, rather than clean up after a campaign has already damaged sender reputation. Pre-send email verification checks syntax, domain and MX records, and whether the mailbox actually exists, so invalid, stale, and disposable addresses are identified and removed in advance.
Run consistently, that check keeps a well-maintained list’s bounce rate close to zero, since almost every remaining bounce becomes an unpredictable soft failure rather than a preventable hard one.
- To calculate your current rate on any list, run it through the bounce checker, which classifies each result as a hard bounce, soft bounce, or clean send.
- To verify addresses before you ever send, use the free email checker or the verification API to catch invalid addresses at signup or before a campaign goes out.
- To monitor bounce rate on an ongoing list, re-verify on a schedule rather than once, since list decay means a clean list today is not guaranteed to stay clean.
Handled this way, bounce rate stops being a metric you discover after the damage is done and becomes a number you control before you send. For teams verifying at scale, where keeping bounce rate under 2% is the difference between reliable inbox placement and a throttled domain, the volume tiers are on the pricing page, and the full pipeline is documented on the email verification page.
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Common questions
Bounce rate, answered
A rising bounce rate is usually the first sign something’s wrong with your list. Here’s what counts as too high, and what to do about it.
What is a good email bounce rate?
Under 2% is generally considered healthy and is the level most mailbox providers expect from a well-maintained list. Between 2% and 5% is a warning zone: deliverability starts to soften, and providers may begin throttling or filtering to inbox.
Above 5% is treated as a signal of a real list-hygiene problem, and sustained rates in that range can trigger blocks or sender-reputation damage that outlasts the campaign that caused it.
How is email bounce rate calculated?
Bounce rate is bounced messages divided by total messages sent, expressed as a percentage: (hard bounces + soft bounces) / total sent × 100. Most email service providers calculate and report this automatically per campaign and per sending domain.
It is worth tracking both the combined rate and the hard-bounce rate on its own, since hard bounces do far more reputation damage per incident than soft bounces do.
What is the difference between hard and soft bounces in the rate?
A hard bounce is permanent: the mailbox does not exist, the domain is invalid, or the server refuses the address outright, and it will never succeed on retry. A soft bounce is temporary: a full inbox, a server briefly down, or a message that is too large, and it often clears on its own.
Both count toward the combined bounce rate, but mailbox providers weigh them differently. A high hard-bounce share reads as poor list hygiene, while a high soft-bounce share often points to a transient delivery issue instead.
Why does a high bounce rate hurt sender reputation?
Mailbox providers read bounce rate as a proxy for how carefully a sender builds and maintains its list. A sender that repeatedly emails invalid or stale addresses looks careless at best and spammy at worst, and providers respond by throttling volume, routing mail to spam, or blocking the sending domain outright.
Because reputation is cumulative and shared across a sending IP or domain, a single bad send can depress deliverability for campaigns that follow, long after the offending list has been cleaned up.
What causes a high email bounce rate?
The most common cause is list decay: roughly 20-30% of email addresses go stale every year as people change jobs or abandon accounts, so an unmaintained list ages into a growing bounce problem. Typos at signup are another steady source, along with purchased or scraped lists that were never opted in and were often stale the day they were bought.
Spam traps and disposable addresses add further risk, since both tend to surface as bounces or complaints rather than clean sends.
How do I lower my email bounce rate?
Verify every address before you send to it, rather than after a campaign has already damaged your reputation. Pre-send email verification checks syntax, domain and MX records, and mailbox existence, so invalid addresses are caught before they ever leave the queue.
Beyond verification, remove addresses that have hard-bounced before, re-permission lists that have gone quiet for a long time, and monitor bounce rate per campaign so a new problem is visible immediately instead of after it has compounded. You can check any list for free with the bounce checker.
Does bounce rate affect inbox placement?
Yes, directly. Bounce rate is one of the core signals mailbox providers use to score sender reputation, alongside complaint rate and engagement. A rising bounce rate typically shows up first as more mail routed to spam, then as throttled sending volume, and in severe cases as an outright block on the sending domain or IP.
Because that scoring is cumulative, keeping bounce rate low is less about any single campaign and more about protecting the reputation every future campaign depends on.