When a subscriber marks your message as spam, the mailbox provider sends you back a message using the ARF format indicating that a complaint has occurred. Their expectation is that you suppress that subscriber from receiving future emails.
Only mailbox providers that offer a complaint feedback loop will send you an ARF message when a complaint occurs - sign up is required. Mailbox providers that don't offer a complaint feedback loop will not send you an ARF message.
Mailbox providers that offer a complaint feedback loop redact personal information in the ARF message, such as the subscriber's email address, for privacy concerns. This makes it difficult to identify and suppress the subscriber.
The only way you can tell which subscriber complained is to add a subscriber ID as an X-header to your email header. When the mailbox provider sends you back the ARF message, the X-header containing your subscriber ID is included. You then take the subscriber ID in that X-header and cross reference it with the subscriber in your database.
- Learn more about what a subscriber ID is and how to implement it
