What is email bounce rate?
Email bounce rate is the percentage of sent messages that were returned as undeliverable. It's calculated as bounced emails divided by total emails sent, multiplied by 100. A rate above roughly 2% signals list-quality problems that hurt deliverability.
How to calculate bounce rate
Bounce rate = (number of bounced emails ÷ number of emails sent) × 100. If you send 10,000 emails and 250 bounce, your bounce rate is 2.5%.
Most analytics separate hard bounces (permanent failures from invalid addresses) from soft bounces (temporary failures). Hard-bounce rate is the more important number for list quality, because it directly reflects how many bad addresses are on your list.
What counts as a good bounce rate
A healthy hard-bounce rate is under 2%; many high-performing senders stay below 1%. Mailbox providers interpret elevated bounce rates as a sign of a purchased, scraped, or neglected list and respond by filtering more of your mail to spam.
Email service providers also enforce thresholds. Sustained bounce rates above their limit can trigger throttling or account suspension, so the metric has real operational consequences beyond analytics.
How to lower your bounce rate
The single most effective lever is verifying addresses — both in real time at the point of capture and in bulk before large sends. This removes invalid addresses before they can bounce.
Complementary practices include using double opt-in to confirm intent, re-verifying inactive segments before re-engagement campaigns, and authenticating your domain so legitimate mail isn't rejected. Mailbeam supports all of these by returning a clear deliverability verdict for every address.
What counts, before you compare the number
Bounce rate is only comparable between two systems if they agree on which status classes are a bounce. Most disagreements start here.
2.X.X Success not a bounce
4.X.X Persistent transient failure soft bounce - retry
5.X.X Permanent failure hard bounce - suppress
bounce rate = bounces / messages accepted for delivery
Two traps in that denominator:
- messages you never sent because a list was pre-filtered
- retries counted as separate sendsA bounce rate without its definition is not a metric: the same list can report very different numbers depending on whether class 4 failures and retries are counted.
Sources
Checked against these sources on .
In practice
Before a 50,000-recipient campaign, a marketer runs the list through Mailbeam's bulk verifier. It flags 1,900 undeliverable addresses, which are suppressed. The campaign goes out to 48,100 addresses with a hard-bounce rate of 0.3% instead of the ~4% it would have hit, protecting inbox placement for the whole list.
Frequently asked questions
Verify emails with confidence
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