Email bounce rate is the share of sent emails that came back undelivered: bounced emails divided by emails sent, times 100. Gmail, Yahoo and Microsoft publish no numeric bounce limit, while sequencers set their own lines: Smartlead's blog calls under 2% good, lemlist says stay under 3%, and Instantly auto-pauses above 5% by default. Fix it in order, starting with verification, because warmup does not fix a bad list (our Warmy review says the same about the tool we feature here).
Some tool links here are affiliate links (disclosure). Nerdy Joe is an affiliate of Warmy and Findymail, a certified Apollo.io Managed Services Partner and a PlusVibe Certified Silver Partner. We have no relationship with Instantly, Smartlead or lemlist beyond affiliate links elsewhere on the site, and we quote their help pages below.
We have not tested any of these tools hands-on. Thresholds and claims below come from each company's own pages as of November 2026.
Bounce rate thresholds at a glance
| Source | What it says about bounces | Type |
|---|---|---|
| Google (Gmail) | No numeric bounce threshold; reduce volume when bounces or deferrals rise | Mailbox provider |
| Yahoo | No numeric threshold; monitor hard and soft bounces, remove invalid recipients promptly | Mailbox provider |
| Microsoft (Outlook.com) | No numeric threshold; regularly remove invalid addresses | Mailbox provider |
| Smartlead (blog) | Under 2% good; 2% to 4% warning zone; 4% to 6% danger zone for a mailbox with 100+ sends | Sequencer |
| lemlist (help center) | Keep under 3%; pause campaigns above 5%; alert at 10%; auto-pause at 50% | Sequencer |
| Instantly (help center) | Default auto-pause above 5%, after 200 emails sent | Sequencer |
| MailReach | Keep bounce rate below 5% | Warmup tool |
| Warmy (warm-up calculator) | "Bounce rates above 2% signal weak engagement" | Warmup tool |
The pattern is clear even though the numbers differ. Under 2% is comfortable by every source here, and above 5% is where tools start stopping your campaigns for you.
Hard bounces vs soft bounces
lemlist's help center gives a plain definition. A hard bounce is permanent: "invalid addresses, typos, closed accounts". A soft bounce is temporary, such as a full inbox or a server issue, and lemlist says recurring soft bounces become hard bounces.
| Hard bounce | Soft bounce | |
|---|---|---|
| Meaning | Permanent failure | Temporary failure |
| Common causes | Address does not exist, typo, closed account, domain gone | Full mailbox, server down, message deferred |
| SMTP reply | Usually a 5xx code | Usually a 4xx code |
| What to do | Remove the address right away | Retry later; remove if it keeps failing |
Smartlead's blog gives a retry rule for soft bounces: try again after 24 to 48 hours, and after three failures across two weeks, treat the address as a hard bounce.
There is a third kind worth naming: policy or block bounces. Since May 5, 2025, Microsoft rejects mail from high-volume senders to Outlook.com that fails its authentication requirements, with the error "550; 5.7.515 Access denied, sending domain [SendingDomain] does not meet the required authentication level." The address is fine; your setup is not.
How to calculate email bounce rate
The basic formula:
Bounce rate (%) = (bounced emails / emails sent) x 100
If you send 1,000 emails and 25 bounce, your bounce rate is 2.5%. If you send 400 and 24 bounce, it is 6%, which would trip most sequencer auto-pauses.
Tools do not all count the same way, so the same campaign can show different numbers:
- Smartlead's help center gives its auto-protection formula as "(total bounce count + latest bounce) / total_lead_count * 100", which divides by leads rather than emails sent.
- Smartlead's blog measures a "good" rate on a rolling 14-day window.
- Instantly only runs its auto-pause check after a campaign has sent at least 200 emails.
- lemlist applies its auto-pause once at least 100 leads have been contacted.
Two habits make the number useful. Track it per mailbox and per campaign, not only account-wide, because one bad list can hide inside a healthy average. And count bounces on first-step emails separately, since follow-ups to the same address rarely bounce again.
What mailbox providers publish
Gmail, Yahoo and Microsoft publish spam-rate and authentication rules. None of them publishes a bounce-rate threshold.
Google (Gmail)
Google's sender guidelines require all senders to set up SPF or DKIM and keep the spam rate reported in Postmaster Tools below 0.3%. Senders of 5,000+ messages a day to Gmail also need DMARC, alignment and one-click unsubscribe. Google advises keeping spam below 0.10% and avoiding "ever reaching a spam rate of 0.30% or higher".
On bounces, Google says that if messages bounce or are deferred, reduce volume until the error rate drops, then increase slowly. It also suggests you may unsubscribe recipients with multiple bounces and confirm each address before subscribing it. No number is given.
Yahoo
Yahoo requires SPF or DKIM for all senders and a spam rate below 0.3%. Bulk senders need SPF, DKIM, DMARC at p=none or stronger, alignment and one-click unsubscribe honored within 2 days.
For bounces, Yahoo recommends monitoring hard and soft bounces, removing invalid recipients promptly and using double or confirmed opt-in. Again, no number.
Microsoft (Outlook.com)
Microsoft's rules apply to domains sending more than 5,000 emails a day to Outlook.com consumer addresses. SPF and DKIM must pass and DMARC must be at least p=none. Its guidance says to regularly remove invalid addresses to reduce complaints and bounces, with no numeric threshold in the announcement.
What Instantly, Smartlead and lemlist say
Sequencers set their own limits because a high bounce rate damages the shared reputation of the mailboxes and domains you send from. Each claim below comes from that company's own page.
Instantly
According to Instantly's help center (article dated October 9, 2026), High Bounce Auto Pause stops a campaign when the bounce rate "exceeds 5%" by default. The check only runs after the campaign has sent at least 200 emails. You can change the threshold or turn it off in Preferences, and after you resume a campaign it will not auto-pause again for 7 days.
Smartlead
Smartlead's blog (published October 28, 2026) says "a good cold email bounce rate is anything below 2% on a rolling 14-day window". It calls 2% to 4% a warning zone and 4% to 6% "the specific danger zone" for a mailbox with 100+ sends. It also says "a program-level bounce rate above 3% starts to affect the shared reputation signals".
Smartlead's help center describes high bounce rate auto protection, which pauses sending at a threshold you set, with 5% and 3% as examples.
lemlist
lemlist's help center (article dated October 8, 2026) says to keep your bounce rate "under 3%" and to pause active campaigns if it "exceeds 5%". lemlist triggers a bounce alert at 10% and auto-pauses campaigns at a 50% bounce rate once at least 100 leads are contacted. A bounce also ends the later email steps for that lead.
Read lemlist's 50% figure as a last-resort safety stop, not a target. Its own advice is the 3% line.
What causes a high bounce rate
Most bounce problems trace back to the list. A few come from setup and sending behavior.
- Invalid addresses. Typos, made-up addresses and addresses that never existed.
- Old data. People change jobs, and an address that was valid when found may close months later.
- Catch-all domains. These servers accept mail for any address at the domain, so a standard check cannot confirm a mailbox exists. Some later bounce.
- Bought or scraped lists. Google's guidelines say not to purchase email addresses from other companies, and these lists tend to carry dead addresses.
- Authentication failures. Missing or broken SPF, DKIM or DMARC can turn into outright rejections, as with Microsoft's 5.7.515 error.
- Volume spikes. Sudden jumps can trigger deferrals and temporary rejections, which is why Google says to reduce volume when bounces rise.
- Blocklisting. A listed domain or IP can see mail refused at some providers.
- Temporary issues. Full mailboxes and server outages cause soft bounces that usually clear on retry.
How to lower your bounce rate: fixes in order
Do these in order. Each later step assumes the earlier ones are done.
1. Verify every list before you send
Verification removes invalid, disposable and risky addresses before they bounce. It is the single fix with the biggest effect on bounce rate, because most hard bounces are bad addresses.
If you also need to find new contacts, Findymail verifies emails in the same step it finds them, and says it refunds credits if your bounce rate exceeds 5%. Our Findymail email verifier guide covers how it handles outside lists, and our roundup of the best email verification tools compares dedicated verifiers.
Warmy also includes verification in its plans. It checks syntax, domain and MX, the mailbox over SMTP, spam traps and complainers, and labels catch-all, disposable and role addresses as Risky. Warmy claims "<1%" typical bounce after cleaning and 99.5% accuracy, with no published methodology.
2. Handle catch-all addresses separately
Do not mix catch-all results into your main send. Verifiers treat them differently: Warmy marks them Risky, and Findymail says it verifies catch-all domains that other tools mark as risky or unknown.
A simple approach:
- Split the list into valid, catch-all or risky, and invalid.
- Delete invalid and disposable addresses.
- Send valid addresses at normal volume.
- Send catch-all addresses in a separate, smaller campaign and watch bounces closely.
- Stop the catch-all segment if its bounce rate climbs past your threshold.
3. Keep the list clean after every send
- Remove hard bounces right away. lemlist already stops later steps for a bounced lead; make sure the address leaves your CRM too.
- Retry soft bounces after 24 to 48 hours and treat three failures across two weeks as a hard bounce (Smartlead's rule).
- Re-verify any list older than a few months before you reuse it.
- Remove recipients with repeated bounces, as Google and Yahoo both suggest.
4. Fix authentication
Set up SPF, DKIM and DMARC on every sending domain, with the From domain aligned. This prevents the policy rejections that show up as bounces at Outlook.com and keeps you inside Gmail's and Yahoo's requirements.
Warmy has free SPF, DKIM and DMARC generators that need no sign-up. If you already use Warmy, its DMARC monitoring alerts on failing sources. Our cold email infrastructure guide covers domain setup end to end.
5. Warm up and ramp volume slowly
New mailboxes and sudden volume jumps attract deferrals. Google's guidelines say to increase volume slowly, start with engaged recipients and avoid spikes. Our email warmup guide covers schedules and timelines.
Warmup comes last in this list on purpose. It builds sending history, but it does not make a dead address deliverable.
Where Warmy fits, honestly
Warmy is a deliverability platform: warmup, placement tests, a seed list, verification and DMARC monitoring in one subscription. For bounce rate, the verification and authentication pieces matter more than the warmup, as our full Warmy review also concludes.
Warmy says plainly that warmup alone does not fix bad addresses, broken authentication or spammy templates. Its high-volume cold outreach guide says to verify every address before launch and to pause if bounces or complaints spike. Its homepage claims a "35% reduction in bounce rates", but gives no methodology, so treat it as a vendor claim.
Where it helps with bounces:
- Verification in the same account as your warmup, using a shared credit balance.
- Free tools without sign-up, including DNS generators, a blacklist checker and an email bounce analyzer listed among its free tools.
- Domain alerts for provider rejections through its Notification Hub, by email, SMS, Slack or webhook.
Where it does not: if your list is bad, no warmup plan changes that. Warmy's comparison pages list plans from $49 to $429 a month as of November 2026, and its pricing page shows only "from $49 a month", so confirm in the app. You can start Warmy's 7-day trial on one mailbox with no card.
A note on Google and warmup: Google's sender guidelines recommend increasing volume slowly to engaged recipients and do not mention warmup tools. Gmail's program policies prohibit automating Gmail in ways that mislead or deceive users, and in 2023, GMass said Google required it to shut down its API-based warmup.
Warmy says it is not affected by those API restrictions and that its warmup emails stay inside its own network; its terms make customers responsible for following their email provider's policies. Google has not published a position on warmup networks specifically.
For the other tool types that help here, see our guide to email deliverability tools.
Pre-send bounce checklist
- [ ] List verified within the last few weeks
- [ ] Invalid and disposable addresses deleted
- [ ] Catch-all addresses split into their own campaign
- [ ] SPF, DKIM and DMARC pass on the sending domain
- [ ] New mailboxes warmed and volume ramped, not spiked
- [ ] Auto-pause on in your sequencer, at a threshold at or below 5%
- [ ] Bounce rate tracked per mailbox and per campaign
- [ ] Copy checked with our spam word checker
If bounces are low but replies are still missing, the problem may be placement, not delivery. Our guide to why emails go to spam covers that diagnosis.
Rather not build the list yourself?
Nerdy Joe is owned by Agency Growth Partners (AGP). AGP builds verified lead lists and runs outbound for agencies, so the verification, catch-all handling and bounce tracking are done before anything sends. If you would rather hand that off, book a call with AGP.
Bottom line
Calculate bounce rate as bounced divided by sent, track it per mailbox, and aim for under 2%, with 3% as a warning line and 5% as a hard stop. Mailbox providers will not give you a bounce number, but they will act on the reputation damage bounces cause.
Fix the list first, then authentication, then volume. If you want warmup, verification and DMARC monitoring in one place, compare Warmy's plans, and read our in-depth Warmy review for every caveat first.
Sources
- Google email sender guidelines: https://support.google.com/mail/answer/81126?hl=en
- Gmail program policies: https://support.google.com/mail/answer/16734397
- Yahoo sender best practices: https://senders.yahooinc.com/best-practices
- Microsoft Outlook requirements for high-volume senders: https://techcommunity.microsoft.com/blog/outlook/strengthening-email-security-outlook-new-requirements-for-high-volume-senders/4399730
- Instantly Help, High Bounce Auto Pause: https://help.instantly.ai/en/articles/9823139-high-bounce-auto-pause-feature
- Smartlead blog, cold email bounce rate: https://www.smartlead.ai/blog/cold-email-bounce-rate
- Smartlead Help, high bounce rate auto protection: https://helpcenter.smartlead.ai/en/articles/274-what-is-high-bounce-rate-auto-protection-in-smartlead
- Smartlead Help, bounce autopause and webhook: https://helpcenter.smartlead.ai/en/articles/210-bounce-autopause-and-webhook
- lemlist Help, understanding and reducing bounces: https://help.lemlist.com/en/articles/4511285-understanding-and-reducing-bounces-a-comprehensive-guide
- MailReach success guide: https://help.mailreach.co/en/article/how-to-get-the-highest-reputation-score-success-guide-vfivvo/
- GMass on shutting down warmup: https://www.gmass.co/blog/warmup-shutting-down/
- Warmy homepage: https://www.warmy.io/
- Warmy pricing: https://www.warmy.io/pricing/
- Warmy vs MailReach comparison (plan table): https://www.warmy.io/compare/warmy-vs-mailreach/
- Warmy email warmup product page: https://www.warmy.io/product/warm-up-email/
- Warmy warm-up calculator: https://www.warmy.io/free-tools/warm-up-calculator/
- Warmy high-volume cold outreach guide: https://support.warmy.io/knowledge/warm-up-for-high-volume-cold-outreach
- Warmy email verification: https://www.warmy.io/product/email-verification/
- Warmy Notification Hub: https://support.warmy.io/knowledge/notification-hub
- Warmy DMARC generator: https://www.warmy.io/free-tools/dmarc-generator/
- Warmy terms of service: https://www.warmy.io/terms-of-service/
- Warmy on GMass and Gmail API restrictions: https://www.warmy.io/blog/why-warmy-is-the-best-gmass-alternative-for-warming-up-email/
- Findymail email verifier: https://www.findymail.com/email-verifier/
- Findymail pricing: https://www.findymail.com/pricing/
Frequently asked questions
What is a good email bounce rate?
For cold email, sequencers draw the line in different places. Smartlead's blog calls under 2% good, lemlist's help center says keep it under 3%, and Instantly's default auto-pause triggers above 5%. Mailbox providers such as Gmail and Yahoo publish spam-rate thresholds, not bounce thresholds.
How do you calculate email bounce rate?
Divide the number of bounced emails by the number of emails sent, then multiply by 100. If 1,000 emails go out and 25 bounce, the bounce rate is 2.5%. Some tools divide by leads contacted instead of emails sent, so check how yours counts.
What is the difference between a hard bounce and a soft bounce?
A hard bounce is a permanent failure, such as an invalid address, a typo or a closed account. A soft bounce is temporary, such as a full inbox or a server problem. lemlist says recurring soft bounces become hard bounces.
Does Gmail have a bounce rate limit?
Google's sender guidelines publish no numeric bounce threshold. They say to reduce volume when messages bounce or are deferred, then increase slowly, and they set a spam-rate limit of 0.3% as reported in Postmaster Tools.
Can email warmup reduce bounce rate?
Not directly. Bounces mostly come from bad addresses, and warmup does not change whether an address exists. Warmy itself says warmup alone does not fix bad addresses, so verify the list first.
Should I remove soft bounces from my list?
Not after one failure. Smartlead's blog suggests retrying soft bounces after 24 to 48 hours and treating an address as a hard bounce after three failures across two weeks. Remove hard bounces right away.
What bounce rate pauses a campaign in Instantly?
Instantly's High Bounce Auto Pause stops a campaign when the bounce rate exceeds 5% by default, once the campaign has sent at least 200 emails. You can change the threshold or turn it off in Preferences.