ARF

ARF stands for "Abuse Reporting Format," a format utilized by mailbox providers to report spam via email to bulk mailers, email service providers, feedback loop service subscribers, and other mailbox providers.

The Internet Engineering Task Force (IETF) developed ARF in response to the rise of email spam and the need for mail operators to exchange abuse reports amongst each other and other parties. Instead of using multiple formats for these reports, the IETF introduced ARF in 2010 to be the standard reporting format, which has also been extended multiple times.

The ARF format is primarily used for reporting abuse in a feedback loop (FBL). An FBL is the form of communication a mailbox provider utilizes to send abuse complaints from their users to the message sender's organization (typically an email service provider).

ARF-formatted email spam reports appear similar to bounced email notifications. They feature the same header as the original reported message and include a human-readable part, a machine-readable part, and the original message. The original message may appear in its entirety or partially (parts may be redacted for legal purposes).

ARF is generic, allowing it to accommodate the reporting of various types of abuse. ARF-formatted reports may contain a "Feedback-Type" field in the machine-readble part that indicates the type of report. The following are possible values for this field:

• Abuse - Spam or another type of email abuse
• Fraud - Fraud or phishing activity
• Virus - Virus found in the message
• Other - Feedback that cannot be categorized by the other values
• Not-spam - Message mistakenly reported as spam

While users are typically responsible for reporting email abuse (reporting it creates the report saved in the ARF format), they will most likely never see the reports. Instead, the message sender's organization receives and reviews the report.