What is the ARF format for feedback?
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When a subscriber hits "This is spam" in their email client, that complaint doesn't just disappear into a void. If the mailbox provider runs a feedback loop, it sends you a structured report about it. ARF is the format that report arrives in.
ARF stands for Abuse Reporting Format. It's defined in RFC 5965 and is the standard way spam complaints get packaged up and sent from mailbox providers to senders who have registered for their feedback loops. The report wraps the original message plus metadata about the complaint in a MIME multi-part structure so you can programmatically identify which message triggered the complaint and which subscriber sent it.
A typical ARF report contains three parts: a human-readable description of the complaint, a machine-readable ARF header block with fields like Feedback-Type, User-Agent, and Reported-Domain, and a copy of the original message (sometimes redacted by the provider).
The practical use: when your feedback loop processor parses an ARF report and finds the original recipient's address in the message headers, you suppress them immediately. This is how responsible senders automatically honor complaints without manual review.
Not all providers use ARF. Gmail stopped offering traditional FBL reports years ago. Yahoo Mail and Outlook still run FBLs, and Yahoo's uses the ARF format. Most complaints you see in Google Postmaster Tools are aggregate rate data, not individual ARF records.
If you want to monitor complaint rates across providers, check your sender reputation tools first. That's where the actionable data lives.
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