Spam Complaint Rate Trend 2026

A critical email marketing metric, the spam complaint rate measures how often recipients flag messages as junk. Calculated as complaints per thousand delivered emails, it directly impacts sender reputation and inbox placement. Email senders, marketing teams, and ISPs use this rate to identify list hygiene issues and content problems. Keeping it below 0.1% protects domain authority, boosts deliverability, and ensures campaigns reach engaged audiences instead of the spam folder.