The email campaign looked successful at first glance—50,000 emails sent, delivery confirmed. Then the bounce report came in: 8,000 hard bounces. A 16% bounce rate. Within hours, their ESP flagged the account. Within days, Gmail started routing their emails to spam. A single campaign with a dirty list had undone months of reputation building.
Bounce rates matter more than most metrics because they compound. High bounces damage reputation, which hurts deliverability, which can cause more bounces as receiving servers become suspicious. The spiral is vicious and recovery is slow.
Here's how to keep bounce rates low and reputation intact.
Prevention at signup
1. Use double opt-in. Require email confirmation before adding addresses to your list. This catches typos, fake addresses, and ensures the person actually wants your email. Yes, it reduces signup conversion. It also dramatically improves list quality.
2. Validate emails in real-time. Check email syntax and domain validity as users type. Catch obvious errors (missing @, invalid TLD) before submission. Some validation services can check mailbox existence in real-time, though this adds latency.
3. Implement CAPTCHA or bot protection. Bots submit fake email addresses. CAPTCHA, honeypot fields, or behavioral analysis reduce bot signups. Fewer fake addresses means fewer bounces.
4. Confirm the address visually. Show users the email they entered and ask them to confirm. "We'll send updates to [email protected]—is this correct?" catches typos the user might otherwise miss.
5. Block disposable email domains. Services like Mailinator and Guerrilla Mail provide temporary addresses that become invalid quickly. Block known disposable domains at signup if your use case warrants it.
List hygiene
6. Remove hard bounces immediately. A hard bounce means the address is permanently invalid. There's no reason to try again. Remove hard bounces from your list after the first occurrence.
7. Handle soft bounces appropriately. Soft bounces are temporary—full mailbox, server down, etc. Retry a few times, but if an address soft bounces consistently (3-5 times over several campaigns), treat it as a hard bounce.
8. Validate your list regularly. Use an email validation service to check your list periodically. Addresses go bad over time—people change jobs, abandon accounts, domains expire. Quarterly validation catches decay before it causes problems.
9. Remove unengaged subscribers. Addresses that never open or click are more likely to become invalid without you knowing. Implement a sunset policy: after 6-12 months of no engagement, either re-confirm interest or remove the address.
10. Watch for spam traps. Spam traps are addresses that should never receive email—either recycled abandoned addresses or addresses that were never valid. Hitting spam traps indicates list quality problems. Validation services can identify some known traps.
Sending practices
11. Warm up new IPs gradually. New sending IPs have no reputation. Start with small volumes to your most engaged recipients, increasing gradually over weeks. Sudden high volume from a new IP triggers suspicion and can cause bounces.
12. Maintain consistent sending patterns. Erratic sending—nothing for months, then a huge blast—looks suspicious. Regular, predictable sending builds trust with receiving servers.
13. Segment by engagement. Send to your most engaged subscribers first. Their positive signals (opens, clicks) build reputation that helps delivery to less engaged segments.
14. Monitor bounce rates by segment. If one segment has higher bounces than others, investigate. Old lists, purchased lists, or specific acquisition channels might be the source of bad addresses.
15. Respect rate limits. Sending too fast can cause temporary bounces as receiving servers throttle you. Implement proper queuing and respect the rate limits of major providers.
When bounces happen
Despite best practices, some bounces are inevitable. How you handle them matters.
Categorize bounces correctly. Not all bounces are equal. "Mailbox full" is temporary. "User unknown" is permanent. "Blocked" might be reputation-related. Your response should match the bounce type.
Investigate patterns. If bounces spike suddenly, something changed. New list source? Infrastructure problem? Blacklisting? Don't just remove the bounces—find and fix the root cause.
Monitor by domain. If bounces are concentrated at specific domains (all @company.com addresses bouncing), you might be blocked by that domain specifically. This requires different remediation than general list quality issues.
Check your authentication. Some bounces result from authentication failures, not invalid addresses. Verify SPF, DKIM, and DMARC are correctly configured and passing.
Acceptable bounce rates
What's "normal" depends on your list and sending patterns, but general benchmarks:
Below 2%: Healthy. Your list hygiene is working.
2-5%: Concerning. Investigate the source of bounces and tighten validation.
5-10%: Problematic. Your reputation is likely suffering. Aggressive list cleaning needed.
Above 10%: Critical. Stop sending until you've cleaned your list. Your ESP may suspend your account.
For transactional email (password resets, order confirmations), bounce rates should be even lower—these go to addresses that just interacted with your system.
The cost of ignoring bounces
High bounce rates don't just waste sending resources. They actively damage your ability to reach valid addresses.
ISPs track bounce rates as a signal of sender quality. High bounces suggest you're not maintaining your list, which correlates with spam behavior. The result: your emails to valid addresses start going to spam.
ESPs monitor bounce rates too. Consistently high bounces can get your account suspended. Even if you're not suspended, you might be moved to lower-quality sending infrastructure.
Recovery is slow. Once reputation is damaged, it takes weeks or months of clean sending to rebuild. Prevention is dramatically easier than remediation.
Frequently asked questions
What's the difference between hard and soft bounces?
Hard bounces are permanent failures—the address doesn't exist, the domain is invalid, etc. Soft bounces are temporary—mailbox full, server temporarily unavailable. Hard bounces should be removed immediately; soft bounces can be retried but should be removed after repeated failures.
Should I try to re-engage bounced addresses?
No. A bounced address is invalid—there's no one to re-engage. Remove it from your list. If you think the bounce was erroneous (rare), you can try once more after some time, but don't keep sending to addresses that bounce.
How do purchased lists affect bounce rates?
Purchased lists typically have very high bounce rates because they're not maintained, contain outdated addresses, and often include spam traps. Using purchased lists is one of the fastest ways to destroy sender reputation. Don't do it.
Can I prevent all bounces?
No. Some bounces are unavoidable—people change jobs, abandon email accounts, companies go out of business. The goal is minimizing bounces through good practices, not eliminating them entirely. A small bounce rate is normal and expected.