ARF Report Parts: Feedback Report & Original Message Explained

What Is an ARF Report and Why Does It Matter for Deliverability?

You send an email. It lands. Then, one day, it doesn’t. No bounce, no error. Just silence. Meanwhile, your inbox placement drops. Your engagement slips. You’re not sure why. One reason might be an ARF report you never saw.

ARF (Abuse Reporting Format) is a standardized way ISPs send you alerts when a recipient flags your email as abusive—whether it’s spam, a phishing attempt, or a policy violation. It’s not a complaint from a user. It’s a forensic packet from the mail system itself.

An ARF report contains two core parts: the Feedback Report, which tells you *what* went wrong (e.g., "marked as spam"), and the original message, which lets you see *exactly* what was sent. You can’t fix what you can’t see. Ignoring ARF means ignoring the most direct signal your sender reputation is under pressure.

Key takeaways

• ARF reports provide direct, standardized alerts from ISPs when your email is reported as abusive
• Understanding the Feedback Report and original message parts is essential for diagnosing deliverability issues
• Missing or misinterpreting ARF reports can lead to prolonged blacklisting, degraded sender reputation, and failed email campaigns

How Does the ARF Message/Feedback Report Structure Work?

ARF (Abuse Reporting Format) reports use a multipart MIME structure with two core parts: a Feedback Report (in plain text or JSON) containing metadata about the complaint, and the original message attached as a message/rfc822 part. This allows abuse analysts to quickly identify the sender, reason for complaint, and inspect the full email content and headers without relying on external logs.

The Feedback Report: What’s Inside

The Feedback Report itself includes key details like the original sender address, the timestamp of the complaint, the receiving IP address, and the specific reason, such as 'spam' or 'phishing'. These fields are standardized under RFC 5965, which defines ARF as a machine-readable format to improve email abuse handling across organizations.

It’s important to note that the report does not include the full content of the message. Instead, it provides a structured summary so that spam and abuse teams can rapidly triage incoming reports. The data is meant to be parsed by automated systems—tools like MailTester help you analyze this data in real time.

The Original Message: Why It Matters

The second part of an ARF report is the original email, attached as a message/rfc822 MIME entity. This includes every header, body, and routing detail that was in the email when it was received. You can examine sender reputation signals, authentication results, and any suspicious behavior—like forged headers or excessive links—directly from the original.

Understanding the original message helps distinguish between accidental spam complaints and genuine abuse. For example, a campaign email might trigger a 'spam' complaint simply because of high volume, but reviewing the full message shows it was properly authenticated and included a working unsubscribe link.

Use cases for this include auditing your sender reputation by checking for inconsistencies between your email practices and user complaints. You can test your messages before sending them to avoid false positives using inbox placement tools like MailTester’s inbox tester. You can also verify your list for validity and risk using bulk verification or the API.

For teams handling large volumes of feedback, having access to both the report and the full message makes investigation faster and more accurate. It’s standard practice in email operations and abuse mitigation, and tools that support ARF parsing are essential for maintaining deliverability.

Decoding the Feedback Report: What Each Field Means

You’re looking at an ARF feedback report? Let’s break down what each field actually tells you. The version shows the ARF standard used, typically 1.0 or 1.1. Reporting-MTA reveals which system flagged the message—like mail.google.com. Source-IP points to where the email originated, crucial for diagnosing misconfigured servers. Reporting-Address is the abuse contact used to send the report, often [email protected]. Complaint-Type specifies why it was flagged (e.g., spam, phishing). Original-To and Original-From show the recipient and sender as seen in the email header. Date logs when the report was generated. These fields are your first clue to why a message was rejected.

Understanding ARF Field Meanings

Each field in a feedback report corresponds to a real event in email delivery or abuse reporting. The table below explains what each field means, based on the official ARF specification (RFC 6591).

Understanding these fields lets you respond faster. If you’re seeing multiple reports with the same Source-IP, investigate your sending infrastructure. If Complaint-Type is "phishing", check for impersonation in your email headers. Bulk list verification can help spot invalid or risky addresses before they trigger abuse reports. Once you know what each field means, you're not just reacting—you’re preventing future issues.

Understanding the Multipart Structure of ARF Reports

ARF reports are MIME multipart messages: they bundle diagnostic data and the original complaint-triggering email into separate parts using unique boundaries. Part 1 is the feedback report, carrying structured abuse metadata like the complaint reason and originating IP. Part 2 is the original message in message/rfc822 format—complete with headers and body—so you can see exactly what was reported. This separation keeps signal (abuse context) distinct from noise (the full message content).

The Feedback Report: Structured Abuse Data

Part 1, typically in text/plain or application/json, contains the abuse report's core details. It includes metadata like the sender’s IP address, timestamp, feedback type (e.g., "spam," "phishing"), and the user’s email address. This structured data is critical for automated analysis—systems can parse it to correlate abuse patterns across domains, IPs, or sending behaviors. RFC 5965 specifies this format, ensuring interoperability across feedback reporting systems.

Let’s say you receive an ARF report with a "spam" flag and a timestamp. You can correlate that with your sending logs and network activity to spot anomalies. If multiple reports cite the same IP or domain within hours, it’s a red flag. Tools like MailTester’s inbox placement checker can help validate whether such triggers affect deliverability in real inboxes.

The Original Message: Full Context for Diagnosis

Part 2 is the full original email, delivered as a message/rfc822 MIME part. It contains every header, body line, and attachment as it was sent. This includes the sender’s address, subject, content-type, and any embedded links—everything that might have triggered the complaint. Having this raw copy lets you verify if content was deceptive, misleading, or outside policy.

For example, if a user reported “phishing,” you can open the original message to check if links point to a malicious site, or if the From address mimics a trusted brand. This raw data is also crucial for legal or compliance reviews. You can cross-reference it with your campaign archives or delivery logs to identify misconfigurations. RFC 822 defines the message format, ensuring consistency across systems.

When you’re troubleshooting a high complaint rate, inspecting both parts together gives full context. A single complaint might seem harmless—but when paired with a consistent source IP and a recurring message layout, it reveals a larger issue. Tools like MailTester’s bulk verification can help catch invalid or risky addresses before they trigger complaints.

While some services may flatten or extract parts of ARF data, keeping the full multipart structure intact preserves fidelity. This structure is industry-standard and supported by major DMARC and abuse reporting platforms like Spamhaus and Google's Postmaster Tools.

Why You Must Analyze the Original Message in ARF Reports

ARF reports alone can’t tell you why an email was flagged as spam—only the original message reveals the full context: the subject line, body content, sender domain, and routing history. Without it, you’re guessing. Spam filters act on patterns, not just bounces, and a legitimate email can trigger a false positive if it contains a suspicious link, overused promotional language, or misaligned headers. The original message lets you distinguish between a benign mistake and a real compromise.

What the Feedback Report Hides

Feedback reports are stripped-down summaries. They tell you a message was rejected and by which filter—but not why. The original message shows you the actual content, including links, sender domain, and email headers. A high-volume newsletter with a clean sender domain might still be blocked if the subject line says “You’re winning $10,000!” or if the body contains excessive capitalization.

Spam filters look at more than just reputation. They analyze the entire message for red flags: URLs that resemble known phishing domains, excessive exclamation points, or mismatches between the “From” address and the domain used in the MAIL FROM command. These are heuristics—not rules—and they can misfire. For example, a promotional email with strong wording might get flagged in a test environment, even if it’s valid. The original message helps you verify if the block was a false positive.

Identifying Real Issues vs. False Positives

When you see an ARF report, you need the original message to determine whether the issue is a genuine threat—a compromised account sending malware—or a legitimate campaign misclassified due to poor formatting or high spam likelihood. That distinction affects your response: a false positive might need a feedback loop update, while a real compromise requires immediate account investigation.

Tools like MailTester’s integrations with platforms like SendGrid and HubSpot can help you test how your messages fare in real inbox environments before sending. You can send test emails to real addresses and see exactly how they land—whether in inbox, spam, or get blocked entirely. This real-world feedback can help you understand what the filter saw and why.

How to Access and Parse ARF Reports Automatically

You can access and parse ARF reports automatically by setting up a dedicated mailbox, using a MIME-aware parser to extract the feedback and original message components, mapping the data fields into your internal systems, and storing the raw message for audit. This process enables real-time abuse trend detection and supports compliance with email reputation standards.

1. Designate a dedicated mailbox such as [email protected] to receive ARF reports. This isolates feedback from operational traffic, reduces noise, and ensures consistent handling of abuse reports—critical for maintaining sender reputation. According to the IETF’s RFC 5965, ARF reports must be delivered to a predefined mailbox to be actionable.
2. Use a mail parser that supports MIME multipart formats. ARF reports are structured as multipart messages, with the feedback report in one part and the original message (usually in the raw, undelivered format) in another. A parser must distinguish between these to extract both components correctly.
3. Map feedback fields to your internal tracking system. Key fields like Reporting-MTA, Arrival-Date, and Original-From should be mapped to your CRM or abuse monitoring tool to correlate report sources with specific campaigns, senders, or list segments.
4. Store the original message in raw format for audit and forensic use. This includes headers, body, and attachments without modification, preserving the full context of the reported message. This raw data is essential when investigating abuse patterns or responding to complaints.

Why This Matters for Deliverability

ARF enables proactive abuse monitoring. Without automated parsing, you risk missing reports that could signal sender reputation issues or list hygiene problems. A 2022 MxToolbox survey found that 57% of ISPs flag domains that don’t act on abuse reports within 48 hours.

Tools to Help You Build This Process

While custom parsing is possible, using tools that support ARF parsing—like those in MailTester’s verification and inbox placement suite—can streamline setup. You can test how your messages interact with filters and spam engines using inbox placement testing, and ensure your data is clean with bulk verification. For programmatic access, the real-time API supports verification at scale.

Automating ARF parsing isn't optional for high-volume senders—it's a baseline of responsible email operations.

Once set up, this process gives you visibility into how your campaigns are perceived by ISPs and users, allowing faster response to potential deliverability risks.

Common Abuse Reasons and Their Root Causes

ARF reports flag abuse when emails fail to meet basic deliverability standards. Common reasons include sending to unsubscribed users, impersonating trusted brands, misrouting from unverified servers, using outdated lists, or sending to high-bounce addresses. These issues stem from poor list hygiene, weak authentication, or insecure sending practices. Let’s break down each one and show how to fix it.

Spam: When Consent Breaks Down

• You’re sending promotional content to recipients who asked to be removed. This triggers filters and complaints. Unsubscribed users don’t just ignore emails—they mark them as spam, harming sender reputation.
• Check your list regularly for consent status. Use double opt-in where possible. A clean list starts with clear permission.
• MailTester’s bulk verification helps identify invalid and unsubscribed addresses before you send.

Phishing: Mimicking Trust

• Phishing emails mimic trusted sources—banks, social platforms, or IT departments—to trick users. The key red flag? A mismatched domain or sender name.
• Even if you’re not a scammer, sending emails that look like a brand can trigger ARF filters. Always authenticate with SPF, DKIM, and DMARC.
• Use real sender names and domains. Never impersonate third parties. Test your email’s authenticity with inbox placement testing.

Misrouting and Server Issues

• Misrouting happens when mail comes from a server with no reverse DNS or improper SPF setup. This breaks trust.
• Compromised or poorly configured servers are common abuse vectors. If your email path isn’t validated, you’re at risk of being flagged.
• Ensure all outbound mail passes basic checks: valid PTR records, proper SPF/DKIM alignment. Use a tool like MXToolbox to audit your server configuration.

List Abuse and Bounce Rates

• Purchasing or using outdated lists floods inboxes with unsolicited mail. Many of these addresses are role-based (e.g., admin@, sales@), catch-all, or invalid.
• Role accounts are notoriously bad for deliverability. Senders often don’t know they’re targeting generic addresses that never open emails.
• High bounce rates—especially hard bounces—directly damage sender reputation. Verify your list in real time to catch invalid, catch-all, or risky addresses early.

We don’t send to addresses that won’t open. That’s the foundation of delivery.

The Human and Technical Mix

• Abuse isn't always malicious—often, it’s poor processes. Misconfigured autoresponders, no list hygiene, or using old data. It's a systems problem, not a single mistake.
• Use a verified, clean list. Regularly scrub your database. A well-hydrated list reduces bounces and increases engagement.
• Check your sender reputation with tools like Spamhaus or DNSBL if you’re seeing spikes in ARF reports.

How MailTester Helps You Detect and Prevent ARF-Triggering Issues

You can use MailTester to catch the most common sources of ARF reports—invalid addresses, role accounts, disposable domains, and risky senders—before they trigger spam complaints or bounces. Its layered verification identifies problems at scale, prevents spam filter red flags, and reduces the chance your IP gets flagged by abuse reports. This proactive cleanup is key to maintaining sender reputation and inbox placement.

Prevent Abuse Before It Starts

Before you send, MailTester’s bulk verification scans entire lists and flags invalid, role-based, and disposable email addresses. These are high-risk contributors to ARF signals—especially when used in campaigns. For example, RFC 7208 outlines how spam traps and invalid addresses can indicate poor list hygiene to receiving servers. Removing these up front reduces the chance your IP gets associated with abuse.

Role addresses like postmaster@ or abuse@ may appear valid but are often used for automated abuse reporting. MailTester detects these so you don’t accidentally send to them. Similarly, disposable domains (like mailinator.com) are short-lived and commonly used to trigger spam detection. Identifying them early avoids hard bounces and potential spam complaints that could lead to ARF reports.

Real-Time Detection and Inbox Simulation

Even with clean data, you can still hit ARF reports if your content or sending behavior triggers filters. MailTester’s real-time API checks live email addresses for catch-all responses and risky patterns—like suspicious keywords or formatting—that increase spam likelihood. Catch-alls, in particular, are notorious for misreporting deliverability issues and contributing to spam trap abuse.

Testing inbox placement with MailTester simulates real-world delivery across major providers like Gmail, Outlook, and Yahoo. It flags content patterns known to trigger spam filters—such as excessive links, aggressive CTAs, or certain text-to-image ratios. This helps you adjust campaigns before launch so you’re less likely to generate complaints that feed into ARF systems.

When ARF signals do surface, MailTester’s in-app AI assistant helps you interpret the data. It cross-references bounce codes, complaint patterns, and known abuse indicators to highlight likely sources—like a high spam complaint rate from a specific domain or a sudden spike in bounces on invalid addresses. This contextual insight makes it easier to respond to abuse reports with accurate data.

Together, these capabilities—bulk verification, API-level checks, inbox testing, and AI-assisted analysis—are designed to reduce the chances of triggering abuse alerts in the first place. For a clean start, try MailTester’s bulk verification tool, or integrate the real-time API into your workflow. See how your messages land with the inbox placement test, and explore integrations with Mailchimp, HubSpot, and others. All with no expiry on your purchased credits—learn more at pricing.

Best Practices for Responding to ARF Reports

If you get an ARF report, act—no matter the domain. Even test emails from a sandbox domain can signal a genuine flaw in your sending setup. The report's Feedback Report and original message contain specific clues about why your email was flagged. Investigate both immediately to sort out if the issue stems from your list hygiene, content, or server configuration. Ignoring it risks being blacklisted or blocked by ISPs.

Immediate Actions After Receiving an ARF Report

• Do not ignore the ARF report—even if it came from a test domain. It might reveal a misconfiguration in your sender setup.
• Download and analyze both the Feedback Report and the original message (including headers). Use tools like MXToolbox to cross-check your IP reputation and check for inconsistencies.
• Check if the issue stems from a bad list (e.g., purchased or outdated addresses). You can verify list quality with real-time tools like MailTester’s bulk verification before sending.
• Review your content for spam triggers—aggressive language, missing unsubscribe links, or excessive links. Tools like MailTester’s inbox placement tester show how your messages appear under real ISP filters.
• Verify your server setup matches established standards: SPF, DKIM, and DMARC records must be correctly configured and aligned.

Long-Term Fixes and Follow-Up

• Update your suppression list immediately. Remove any address that triggered the ARF report, even if it’s a rare bounce.
• Discontinue sending to inactive subscribers. If someone hasn’t engaged in 12+ months, treat them as high risk unless you have a re-engagement campaign.
• Sanitize sender headers. Remove or fix malformed From, Reply-To, or Return-Path values that confuse ISPs.
• Document every action taken. Note the date, the report source, the root cause, and the corrective step.
• Where possible, contact the reporting ISP to confirm resolution. Some major providers, like Comcast or Yahoo, may respond to verified feedback and lift restrictions.

Reputation isn’t built overnight—it’s maintained by consistent response to every signal, even the smallest.

ARF reports are not just noise. They are direct feedback from the gatekeepers of inbox placement. Treat each one as a diagnostic tool. By responding quickly, systematically, and transparently, you protect your sender reputation and stay out of the spam traps. Tools like MailTester’s verification API can help you avoid sending to bad addresses before they trigger ARF reports in the first place.

The Bottom Line: ARF Reports Are a Deliverability Safety Net

ARF reports are not just automated warnings—they are direct feedback from ISPs about how your messages are being received. Each report reveals specific reasons why an email was marked as spam, offering clarity on sender behavior that impacts inbox placement.

Why Every ARF Report Matters

• Ignoring ARF reports increases the risk of blacklisting and harms sender reputation over time.
• Regular analysis identifies patterns—such as high spam complaints or malformed headers—that signal deeper deliverability issues.
• Proactive review of the original message and feedback report helps isolate sender-side problems from ISP filtering quirks.

Automation and tools like MailTester transform raw ARF data from noise into actionable intelligence. By cross-referencing reported emails with real-time verification and reputation analysis, you can detect invalid addresses, catch-all recipients, and disposable domains before they degrade your sender reputation.

Keep reading

• Deliverability monitoring, metrics and reporting (complete guide)
• What Is ARF Abuse Reporting Format RFC 5965 Explained Simply
• What Is Panel Data in Email Deliverability? Explained
• How to Build a Deliverability Dashboard That Works in 2026
• How to Use SNDS Automated Data Access URL for Monitoring

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Frequently asked questions

What is the purpose of an ARF report?

An ARF report notifies senders when their email is flagged as abusive by an ISP. It contains metadata and the original message to help diagnose and resolve the issue.

What does the Feedback Report in an ARF contain?

It includes the reporting MTA, source IP, complaint type, original sender and recipient, timestamp, and the abuse reason (e.g., spam or phishing).

Why is the original message part included in ARF reports?

It provides context to verify whether the content matches the abuse claim, helping distinguish between false positives and actual violations.

Can ARF reports be faked or forged?

Legitimate ARF reports are generated by ISPs with proper authentication. However, forged reports can be sent—reputable ISPs validate them before delivery.

How do I set up ARF report monitoring?

Create a dedicated email address (e.g., [email protected]), configure your server to accept incoming ARF reports, and use a parser to extract feedback and original message components.

What is the difference between ARF and DSN?

ARF reports are about abuse complaints (e.g., spam), while DSNs (Delivery Status Notifications) report delivery failures like bounces or timeouts.

How can I reduce the number of ARF reports I receive?

Maintain clean lists, honor unsubscribe requests, verify email addresses before sending, and monitor content for spam-like patterns.

Does MailTester process ARF reports?

MailTester doesn’t receive ARF reports directly, but it helps prevent the conditions that trigger them through email verification and deliverability testing.

Why do some ARF reports include the original message in JSON format?

Some ISPs use JSON as the Feedback Report format for machine readability, though the original message remains in message/rfc822 format.

How long should I keep ARF reports for audit purposes?

Store ARF reports and related data for at least 6 months to support compliance and investigative needs.

Is ARF part of DMARC?

ARF is not part of DMARC, but DMARC policies help enforce alignment and authentication, reducing the likelihood of spoofing that can trigger abuse reports.

Can ARF reports cause blacklisting?

Not by themselves—but ignoring repeated ARF reports signals poor hygiene, increasing the risk of being blacklisted by ISPs.