In the context of cold email, a feedback loop is a mechanism through which internet service providers (ISPs) provide email senders with information about complaints made by recipients regarding their emails. When a recipient marks an email as spam or junk, the ISP records this complaint and, if the sender is enrolled in the ISP's feedback loop program, reports it back to the sender. This information allows the sender to identify and remove recipients who do not want to receive their emails, helping to maintain a clean email list and improve sender reputation. By monitoring and acting on feedback loop data, senders can reduce spam complaints, enhance deliverability, and ensure that their email campaigns are more relevant and compliant with anti-spam regulations.