A feedback loop is a simple but critical mechanism. It's a way for an inbox provider (like Gmail, Outlook) to automatically tell you when a recipient marks your email as spam.
You don't "set it up" yourself. You subscribe to it through the major providers' postmaster programs. They then send you a near-real-time notification (usually a formatted email) when a user hits "report spam."
Key points:
* It's the most direct signal for list hygiene. Those users are toxic to your sender reputation.
* You must process these reports and suppress the reported addresses immediately.
* Most ESPs offer this as a built-in feature. You just need to authenticate your domain (SPF, DKIM, DMARC) and enroll in the respective feedback loop programs.
Without it, you're flying blind on reputation decay.
Show me the methodology.