Bounce Rate Above 2%? What to do in the Next 24 Hours

Bounce rate: 15%.

• Check your ESP report

  Start with the bounce report for the campaign that crossed 2%. Check bounce types, SMTP response codes, affected domains, and when the bounce rate spikes.
  
  Look for responses including “550 User Unknown,” “mailbox does not exist,” or “domain not found” in reports. Temporary deferrals may indicate delivery issues that can be cleared without permanently invalidating the affected recipient address immediately.
  
  Adobe Marketo Engage categorizes codes in the 400 range as soft bounces, and those in the 500 range as hard bounces. These include 550 for mailboxes, 5.1.1 for permanent email delivery error, and 421 or 450 for failures. Different ESPs may have different codes, so check each message against your ESP's code before determining the next steps.

• Pause the active campaign

  Once you confirm the spike, pause the affected campaign. This prevents additional sends while you identify the affected contacts and source. Keep the campaign paused until the segment has been reviewed and cleaned.

• Isolate bounced contacts

  Keep them out of your active sending list while you investigate. Record the campaign, list source, import date, bounce type, and recipient domain.

• Verify and suppress hard bounce contacts

  For hard bounces, verify affected contacts before sending again to confirm which addresses remain unsafe for delivery. Clearout Email Verifier can check bounced segments in bulk and identify invalid, risky, disposable, and catch-all email addresses. If verification confirms an address is invalid, keep it suppressed.
Hard bounces usually indicate permanent delivery problems, while soft bounces are often temporary. For more details, check our bounce rate guide.

• Review soft-bounced contacts separately

  Do not suppress soft bounces immediately; review the delivery response before deciding whether the address needs suppression. Temporary deferrals, mailbox-full errors, and receiving-server issues can clear without permanently invalidating affected recipient addresses for delivery.
  
  Hold these contacts separately and retry according to your ESP's guidance after reviewing delivery responses. If an address repeatedly fails, follow your ESP's suppression rules instead of using a retry count again.

• Review recent imports

  If one source accounts for most of the bounces, quarantine that source and run its remaining contacts through Clearout Email Verifier before using them again.
  
  Check:
  
  
  • CSV imports
  • Event lists
  • Webinar registrations
  • Form submissions
  • CRM imports
  • Third-party data
  • Recently synced contacts
  Then, compare the email bounce rate for each source separately.
  
  If one source accounts for most of the bounces, quarantine that source and verify its remaining contacts before using them.

• Compare list segments

  Next, break the affected contacts into smaller groups.
  
  Check the campaign, import date, data source, recipient domain, contact type, and sending domain.
  
  If several unrelated segments show the same increase, expand the investigation to your sending setup and recent database changes. A spike concentrated in one segment usually points toward that segment's source or recent data change.

• Review bounce codes

  If you have a 15% email bounce rate, start deleting contacts or changing your email strategy, and dig into the bounce codes. Look at the SMTP responses or the classifications provided by your ESP. Some bounces happen because the email address no longer exists.
  
  Others are caused by the recipient's mailbox being full, server temporarily unavailable, or the message being blocked due to policy reasons. If you're looking for a breakdown of common responses, check out our email bounce codes guide.

• Send verified contacts first

  For the first recovery batch, use verified contacts from unaffected segments not part of the problematic campaign. Keep confirmed invalid addresses suppressed and exclude contacts from the source responsible for the original spike.
  
  For catch-all results, use Clearout Email Verifier to assess whether those addresses are safe to send. It helps you avoid invalid email addresses entering your list.

• Review recovery results

  Watch the bounce rate as the recovery batch goes out.
  
  Compare it with the original campaign and check whether the same domains or sources are failing again. If the rate rises, pause and investigate before expanding volume.

• Document the failed source

  Document where the problematic contacts came from, such as forms, imports, purchased lists, integrations, or manual uploads. Record import date, list type, affected segment, source, and bounce pattern to trace the issue accurately.
  
  Once you identify a recurring problem source, flag it in your CRM or list workflow. This makes it easier to verify future imports before they enter active campaigns.

• Verify every new list

  Verify new contacts with Clearout Email Verifier before adding them to an active sending segment. It supports bulk verification and real-time validation, helping check contacts before they enter your sending workflow. Pay particular attention to event lists, form exports, CRM imports, and third-party datasets.

• Set thresholds for different bounce signals

  Do not rely on the overall bounce rate alone. Track hard bounces, soft bounces, SMTP responses, and recipient-domain patterns separately. A sudden concentration of 5xx SMTP responses or failures from one domain can reveal a data or delivery problem before the overall rate becomes significant.

• Control risky addresses before campaigns

  Do not automatically treat every unknown or catch-all address as safe to send. Use deeper verification when an address needs additional validation before entering a campaign. Clearout's Deep Verify can provide a Safe to Send result for uncertain addresses, giving you another checkpoint before delivery.

• Keep suppression logic connected to your sending workflow

  Automatically suppress confirmed invalid addresses so they cannot re-enter future campaigns through another import or workflow. Also preserve bounce and verification status in your CRM, allowing future campaigns to exclude previously identified problem addresses.

• Monitor recipient-domain patterns

  Review bounce patterns by recipient domain instead of looking only at campaign-level averages. If failures suddenly concentrate around specific domains, investigate their SMTP responses before increasing campaign volume or changing your sending strategy.

• Audit your acquisition and enrichment sources

  Track where new contacts enter your database. If one source repeatedly produces invalid contacts, fix the source or verify its data before the next import.
  
  Compare verification results across forms, events, CRM imports, enrichment providers, and other acquisition sources. A recurring pattern can identify which source needs correction rather than repeatedly cleaning the resulting contacts.