Metrics
Complaint Rate
The percentage of recipients who mark your email as spam. Should be kept below 0.1%.
Definition
Complaint rate is the percentage of recipients who mark your email as spam. It's calculated as (spam complaints ÷ emails delivered) × 100. Major mailbox providers like Gmail and Yahoo consider a complaint rate above 0.1% (1 in 1,000) as problematic. Rates above 0.3% can trigger immediate deliverability issues. Complaint rates are tracked through Feedback Loops (FBLs) from ISPs.
Examples
10,000 emails sent, 5 complaints = 0.05% (healthy)10,000 emails sent, 50 complaints = 0.5% (problematic)
Pro Tip
Monitor complaint rates closely. A sudden spike often indicates list quality issues or content that recipients find irrelevant.