What Is Bounce Rate?
Bounce rate is the percentage of sent emails that could not be delivered and were returned by the receiving server. It splits into hard bounces (permanent failures) and soft bounces (temporary). A high bounce rate signals poor list quality and quickly damages sender reputation.
Every bounce is a delivery failure the receiving server reports back to you. Providers watch bounce rates closely because sending to many invalid addresses is a hallmark of spammers using scraped or purchased lists.
Keep total bounce rate below 2%, and hard bounces well under that. Crossing 5% often triggers throttling or blocks. The fix is list hygiene: validate addresses before sending, remove hard bounces immediately, and avoid buying lists.
Bounces also inflate cost and skew metrics — undeliverable sends waste sending quota and distort open/reply calculations. Treat a rising bounce rate as an early warning that your list or authentication needs attention.
How bounce rate is calculated
Bounce rate is the number of bounced messages divided by the total number sent, expressed as a percentage. If you send 1,000 emails and 30 bounce, your bounce rate is 3%. Providers and email tools track it per campaign and as a rolling average, because the trend matters as much as any single send.
Every bounce is a delivery failure the receiving server reports back with an SMTP status code. Those codes split bounces into two categories — permanent (hard) and temporary (soft) — and the distinction drives how you should respond. Mailbox providers watch bounce rates closely because sending to many invalid addresses is a hallmark of spammers using scraped or purchased lists.
Hard bounces vs soft bounces
A hard bounce is a permanent failure (5xx SMTP code): the address does not exist, the domain is invalid, or the server has permanently rejected you. Hard-bounced addresses must be suppressed on the first bounce and never mailed again — repeated sends to dead addresses signal poor hygiene and often mean you are hitting spam traps.
A soft bounce is a temporary failure (4xx SMTP code): a full mailbox, a server that is briefly down, greylisting, or an oversized message. Sending servers retry soft bounces automatically over 24–72 hours. A single soft bounce is harmless, but an address that soft-bounces repeatedly across campaigns should be treated as undeliverable and suppressed.
How to reduce your bounce rate
Bounce rate is a list-quality problem more than a sending problem. Validate every address before you send using a verification service, use double opt-in so only real addresses enter your list, and remove hard bounces immediately and automatically. Never buy or scrape lists — they are the fastest route to a high bounce rate and spam-trap hits.
Also confirm your authentication is correct: some 5xx rejections are policy bounces caused by missing SPF, DKIM, or DMARC rather than bad addresses. Treat any rising bounce rate as an early warning that your list, your authentication, or your sending reputation needs attention.
Bounce rate thresholds (healthy vs risky)
| Bounce rate | Status | What it means | Action |
|---|---|---|---|
| Under 2% | Healthy | Normal for a well-maintained list | Keep validating and suppressing bounces |
| 2–5% | Warning | List quality is slipping | Clean the list; re-verify addresses |
| Over 5% | Critical | Often triggers throttling or blocks | Stop sending; validate list before next send |
| Hard bounces > 2% | Critical | Strong sign of a stale or bought list | Suppress all hard bounces; verify sources |
Frequently asked questions
What is a good bounce rate for email?
A healthy email bounce rate is under 2%, with hard bounces well below that. Between 2% and 5% is a warning sign that list quality is slipping, and crossing 5% often triggers throttling or blocks from mailbox providers. The lower your bounce rate, the better your sender reputation.
What is the difference between a hard bounce and a soft bounce?
A hard bounce is a permanent failure (5xx code) — the address is invalid or the domain does not exist — and must be suppressed immediately. A soft bounce is a temporary failure (4xx code) such as a full mailbox or a server briefly down, and is retried automatically before being treated as undeliverable.
How do I reduce my email bounce rate?
Validate addresses before sending, use double opt-in to keep bad addresses off your list, and remove every hard bounce immediately. Avoid buying or scraping lists, and confirm SPF, DKIM, and DMARC are correct so policy rejections do not inflate your bounce rate. Good list hygiene is the single biggest lever.
Why does a high bounce rate hurt deliverability?
Mailbox providers treat a high bounce rate as evidence of a bought or scraped list, which is classic spammer behavior. It damages sender reputation, can trigger throttling or outright blocks above 5%, and often correlates with hitting spam traps — all of which push future mail toward the spam folder.
How is bounce rate calculated?
Bounce rate is the number of bounced messages divided by the total number sent, shown as a percentage. Sending 1,000 emails with 30 bounces gives a 3% bounce rate. It is tracked per campaign and as a rolling average, since a rising trend is an early warning of list or authentication problems.
MailPilot warms up mailboxes with a clean network of real recipients, so warmup traffic never inflates your bounce rate, and its monitoring flags deliverability dips early.
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