CleverReach GmbH & Co. KG This document describes a method to allow a mail sender to specify a complaint feedback loop address as an email header and how a mail receiver can use it. This document also defines the rules for processing and forwarding such a complaint. The motivation for this arises out of the absence of a standardized and automated way to provide a complaint feedback loop address to mailbox providers. Currently, providing and maintaining such an address is a manual to a time-consuming process for mail senders and mailbox providers.