What it is
Some mailbox providers report when a recipient marks a message as spam. Complaint handling converts those reports into suppression and operational insight.
Why it matters
Mailing a complainer again ignores an explicit negative signal and increases the chance that all mail from the stream is filtered.
How to implement
Register authenticated domains for feedback loops, map reports to internal recipients without leaking personal data, suppress immediately, and segment metrics by source, campaign, and acquisition path.
Common mistakes
- Treating complaints as a dashboard metric but not a suppression event.
- Logging entire message bodies unnecessarily.
- Averaging transactional and marketing streams together.
Verification
Inject a synthetic complaint into the processing path and confirm the address cannot be queued again from any sending application.