How should I handle bounced transactional emails?

Handle bounced transactional emails as a deliverability and customer-experience issue, not just a logging issue. A good approach is:

1. Classify the bounce

   • Hard bounce: permanent failure, e.g. invalid address, unknown user, blocked domain.
   • Soft bounce: temporary failure, e.g. mailbox full, server down, message too large.
   • Complaint / block / defer: sometimes treated separately by ESPs; important for reputation.

2. Stop sending to hard-bounced addresses

   • Immediately suppress hard-bounced addresses from future sends.
   • Don’t keep retrying invalid addresses.
   • If a user can change their email, let them update it in-app and verify the new one.

3. Retry soft bounces with limits

   • Retry a few times with exponential backoff.
   • Stop after a reasonable threshold and mark as undeliverable if it keeps failing.
   • Avoid infinite retry loops.

4. Monitor patterns

   • Watch bounce rate by domain, campaign type, and sender reputation.
   • Spikes can indicate:
     • bad list hygiene
     • DNS/authentication issues (SPF, DKIM, DMARC)
     • reputation problems
     • provider outages

5. Make transactional delivery resilient

   • Use a reputable email service provider.
   • Authenticate your domain properly:
     • SPF
     • DKIM
     • DMARC
   • Keep sending infrastructure separate from marketing if possible.

6. Store bounce reasons and metadata

   • Save the SMTP code, provider reason, timestamp, and message ID.
   • This helps you distinguish transient vs permanent failures and debug issues.

7. Notify the user when appropriate

   • If the email is essential, inform the user in-app that delivery failed and prompt them to update their address.
   • Be careful not to expose sensitive delivery details.

8. Protect account security

   • For transactional messages like password resets, don’t rely on email alone if bounce rates are high.
   • Offer fallback methods: SMS, authenticator app, support flow, or re-verification.

9. Set up suppression and reconciliation

   • Maintain a suppression list for hard bounces and complaints.
   • If a user later corrects their email, remove suppression only for the new verified address, not the old one.

10. Track business impact

• Measure:
  • bounce rate
  • delivery rate
  • time to deliver
  • resend success rate
  • user recovery actions
• Use these metrics to improve UX and email hygiene.

A simple policy that works well:

• Hard bounce: suppress immediately.
• Soft bounce: retry 3–5 times over 24–72 hours.
• Still failing: suppress and notify user in-app.

If you want, I can also give you:

• a bounce-handling workflow/diagram
• a database schema for tracking bounces
• sample code/pseudocode for processing webhook bounce events