Email Glossary

Complaint Rate

Complaint rate is the percentage of delivered emails that recipients report as spam, calculated as complaints / delivered. Mailbox providers track complaint rates per sender and per IP. Rates above 0.1% (1 complaint per 1,000 emails) trigger reputation penalties. Gmail's threshold is particularly strict.

How to Reduce Complaints

  • ●Easy unsubscribe - Make the unsubscribe link prominent and one-click
  • ●List-Unsubscribe header - Add the header for Gmail/Yahoo native unsubscribe button
  • ●Relevance - Send content subscribers actually want
  • ●Frequency - Don't send too often
  • ●Expectation setting - Tell subscribers what they will receive and how often
  • ●Re-engagement - Remove or re-engage inactive subscribers before they mark you as spam

Related Terms

Bounce Rate

The percentage of sent emails that couldn't be delivered to the recipient.

Sender Reputation

A score ISPs assign to your sending IP and domain based on email behavior.

Suppression List

A list of email addresses that should never receive emails, including unsubscribes, bounces, and complaints.

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