When an email recipient identifies an email message as spam or junk by clicking the "report spam" or "mark as junk" button within their email reader.
A complaint is when an email recipient identifies an email message as spam or junk by clicking the "report spam" or "mark as junk" button within their email reader.
A sender's complaint rate is calculated by dividing the total number of emails received by the ISP by the number of complaints reported by that ISP's customers.
Higher numbers of complaints can negatively impact your email deliverability.
To get more information please check out our Email Infrastructure Guide.