email bounces and complaint tracking for transactional mail

For transactional email, you should track both bounces and complaints, because they affect deliverability differently and can indicate different issues.

What to track

1) Bounces

• Hard bounces: permanent failures, e.g. invalid address, domain doesn’t exist.
• Soft bounces: temporary failures, e.g. mailbox full, server unavailable.

Why it matters:
High hard bounce rates usually mean bad list hygiene or data quality issues. Repeated soft bounces can indicate recipient issues or throttling.

2) Complaints

• Recipient marks email as spam or junk.

Why it matters:
Complaint rates are a major signal to mailbox providers and can hurt sender reputation quickly, even for transactional mail.

Best practices for transactional mail

• Track bounce reason codes and categorize them.
• Track complaint events separately from bounces.
• Suppress hard-bounced addresses immediately.
• Watch complaint spikes by sender, template, and customer segment.
• Correlate with message type: password reset, receipt, OTP, notifications, etc.
• Monitor deliverability metrics:
  • delivery rate
  • bounce rate
  • complaint rate
  • open/click rate if applicable
  • latency/time-to-delivery

What “good” looks like

• Hard bounce rate: very low, ideally under 1%
• Complaint rate: extremely low, often below 0.1% is a common target

Extra note for transactional mail

Even though transactional emails are expected, users can still complain if:

• they receive messages they didn’t request
• frequency is too high
• content is confusing or misleading
• messages look promotional instead of functional

If you want, I can also provide:

1. a metrics schema for bounce/complaint tracking, or
2. an AWS SES / SendGrid / Postmark implementation example.