Spam Complaint Rate

Spam complaint rate is the percentage of delivered emails marked as spam by recipients. It matters because complaint spikes quickly damage sender reputation and reduce inbox placement. Teams usually monitor complaint rate by campaign, segment, and acquisition source to identify where expectation mismatch is highest. Practical controls include clear signup intent, strong list hygiene, relevant targeting, and an easy unsubscribe path. Thresholds vary by provider, so use your ESP and ISP feedback as the operational baseline. A common mistake is optimizing only opens and clicks while ignoring complaint trends that silently hurt long-term deliverability.