|
|
|
|
|
|
IETF RFC 6449
Last modified on Thursday, November 17th, 2011
 Permanent link to RFC 6449
 Search GitHub Wiki for RFC 6449
 Show other RFCs mentioning RFC 6449
Internet Engineering Task Force (IETF) J. Falk, Ed.
Request for Comments: 6449 Messaging Anti-Abuse WG
Category: Informational November 2011
ISSN: 2070-1721
Complaint Feedback Loop Operational Recommendations
 Abstract
Complaint Feedback Loops similar to those described herein have
existed for more than a decade, resulting in many de facto standards
and best practices. This document is an attempt to codify, and thus
clarify, the ways that both providers and consumers of these feedback
mechanisms intend to use the feedback, describing some already common
industry practices.
This document is the result of cooperative efforts within the
Messaging Anti-Abuse Working Group, a trade organization separate
from the IETF. The original MAAWG document upon which this document
is based was published in April, 2010. This document does not
represent the consensus of the IETF; rather it is being published as
an Informational RFC to make it widely available to the Internet
community and simplify reference to this material from IETF work.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It has been approved for publication by the Internet
Engineering Steering Group (IESG). Not all documents approved by the
IESG are a candidate for any level of Internet Standard; see Section
2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 6449.
Falk Informational PAGE 1 
RFC 6449 CFBL Recommendations November 2011
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may not be modified, and derivative works of it may not
be created, except to format it for publication as an RFC or to
translate it into languages other than English.
Falk Informational PAGE 2
RFC 6449 CFBL Recommendations November 2011
Table of Contents
1. Overview ........................................................4
2. Glossary of Standard Terms ......................................5
3. Mailbox Providers and Feedback Providers ........................9
3.1. Benefits of Providing Feedback .............................9
3.2. Collecting Complaints .....................................10
3.3. Creating Reports ..........................................11
3.4. Policy Concerns ...........................................11
3.4.1. Privacy and Regulatory Compliance ..................11
3.4.2. Terms of Use .......................................12
3.5. Handling Requests to Receive Feedback .....................12
3.5.1. Application Web Site ...............................13
3.5.2. Saying No ..........................................14
3.5.3. Automation .........................................14
3.6. Ongoing Maintenance .......................................15
3.6.1. IP Validation ......................................15
3.6.2. Email Address Validation ...........................16
3.6.3. Feedback Production Changes ........................16
4. Feedback Consumers .............................................16
4.1. Preparation ...............................................17
4.2. What You'll Receive .......................................18
4.2.1. Feedback Reports ...................................18
4.2.2. Administrative Messages ............................18
4.2.3. Report Cards .......................................18
4.3. Handling Feedback Messages ................................19
4.3.1. Unsubscription or Suppression ......................20
4.3.2. Trending and Reporting .............................21
4.4. Automatically Handling an Incoming Feedback Stream ........22
5. Conclusion .....................................................25
6. Acknowledgments ................................................26
6.1. About MAAWG ...............................................26
7. Security Considerations ........................................26
8. Informative References .........................................26
Appendix A. Abuse Reporting Format (ARF) ..........................28
A.1. A Brief History ............................................28
A.2. Structure of an ARF Message ................................28
Appendix B. Using DKIM to Route Feedback ..........................29
Appendix C. Unsolicited Feedback ..................................30
C.1. Guidelines .................................................30
C.2. Pros .......................................................30
C.3. Cons .......................................................31
Falk Informational PAGE 3
RFC 6449 CFBL Recommendations November 2011
1. Overview
The intent of a Complaint Feedback Loop is to provide Feedback
Consumers with information necessary to mitigate Spam or the
perception of Spam. Thus, feedback was originally only offered to
mailbox, access, and network providers -- in other words, to ISPs --
who would use the feedback to identify network compromises and
fraudulent accounts or to notify their downstream customer that there
may be a problem.
Senders of bulk, transactional, social, or other types of email can
also use this feedback to adjust their mailing practices, using Spam
Complaints as an indicator of whether the Recipient wishes to
continue receiving email. Common reactions often include refining
opt-in practices, mailing frequency, list management, message
content, and other measures. Over time, this has become the Feedback
Consumer use case most often discussed at MAAWG meetings and other
industry events -- but readers are cautioned that it is not the sole
use for feedback.
[ Feedback Consumer Database ]
|
V
[ User ] [ Mailbox ] [ Feedback ]
[ Reports ]--->[ Provider ]--SMTP-->[ Provider ]
[ Spam ] | |
V V [ Feedback ]
[Spam Filter Rules] [ ARF Message ]--SMTP-->[ Consumer ]
Figure 1
When an End User of a Mailbox Provider issues a Spam Complaint, the
Feedback Provider sends a report to the Feedback Consumer. This
report may include the Full Body of the original email or (less
commonly) only the full header of the original email. Some Feedback
Providers will redact information deemed private, such as the Message
Recipient's Email Address.
Ensuring that Feedback Messages are only sent to authorized Feedback
Consumers is the responsibility of the Feedback Provider, with the
identity of each message Sender generally determined from the SMTP
session's connecting IP address or a message's DomainKeys Identified
Mail (DKIM) signature domain, both of which are hard to forge. This
is important because Spammers and other miscreants may also attempt
to apply for Feedback Loops on networks not belonging to them, in an
attempt to steal Email Addresses and other private personal or
corporate information.
Falk Informational PAGE 4
RFC 6449 CFBL Recommendations November 2011
It is the responsibility of the Feedback Consumer to identify the
source and nature of the original message in the reports they receive
and take any appropriate action. The Feedback Provider does not make
any claims or judgments about the validity of the complaint, beyond
whatever technical data the Feedback Provider has themselves
included. Every complaint is forwarded to the Feedback Consumer
without human review, without any additional application of filters;
thus, some individual reports may prove not to be actionable.
The Feedback Consumer and the Feedback Provider will each evaluate a
Spam Complaint for validity and take whatever action deemed necessary
from their own perspective and, in most cases, will not communicate
with each other which actions were (or were not) taken. Similarly,
it is rare for any party to communicate further with the End User who
initiated the complaint.
2. Glossary of Standard Terms
Wherever possible, these terms are derived from [RFC 5598].
o Abuse Reporting Format - The standard format for Feedback
Messages, defined in Appendix A and [MARF].
o Access Provider - Any company or organization that provides End
Users with access to the Internet. It may or may not be the same
entity that the End User uses as a Mailbox Provider.
o Application for Feedback Loop - the process, manual or online, by
which a prospective Feedback Consumer requests to receive a
Feedback Loop from a particular Feedback Provider.
o ARF -- See "Abuse Reporting Format".
o ARF Report -- See "Feedback Message".
o Body - See "Full Body".
o Complaint or Complaint Message - See "Feedback Message".
o Complaint Feedback Loop - See Overview and Taxonomy section.
o Complaint Stream - See "Feedback Stream".
o Delivery - See "Message Delivery".
o DKIM - DomainKeys Identified Mail, further described in the MAAWG
email authentication white paper "Trust in Email Begins with
Authentication" [Trust] and [DKIM].
Falk Informational PAGE 5
RFC 6449 CFBL Recommendations November 2011
o End User - A customer of a Mailbox Provider or Access Provider.
o Envelope Sender - The Email Address included as the argument to
the [SMTP] "MAIL" command during transfer of a message.
o Email Address - A string of the form user@domain, where the domain
(after the @ symbol) is used to determine where to transfer an
email message so that it may be delivered to the mailbox specified
by the username (before the @ symbol). The precise technical
format of an Email Address is defined in [SMTP]. Email delivery
can be a complex process and is not described further in this
document.
o Email Service Provider (ESP) - A provider of email sending
services; the ESP is often a Message Originator working on behalf
of a Message Author. MAAWG uses the term "ESP" solely for this
definition and does not refer to a Mailbox Provider for End Users
as ESPs.
o FBL - The acronym "FBL" (Feedback Loop) is intentionally not used
in this document.
o Feedback or Feedback Stream - A set (often a continuous stream) of
Feedback Messages sent from a single Feedback Provider to a single
Feedback Consumer.
o Feedback Consumer - A Recipient of the Feedback Messages, almost
always on behalf of or otherwise associated with the Message
Originator. Often the Message Originator and Feedback Consumer
are the same entity, but we describe them separately in this
document because they are each responsible for different parts of
the Complaint Feedback Loop process, as demonstrated in the
flowchart in the Overview section.
o Feedback Loop - See Complaint Feedback Loop.
o Feedback Message - A single message, often using the Abuse
Reporting Format defined above and outlined in Appendix 1, which
is part of a Feedback Stream.
o Feedback Provider - The Sender of the Feedback Messages, almost
always on behalf of or associated with the Mailbox Provider.
Often the Mailbox Provider and Feedback Provider are the same
entity, but we describe them separately in this document because
they are each responsible for different parts of the Complaint
Feedback Loop process. In some instances, the Feedback Provider
may be operating solely on behalf of the Message Recipient,
without any direct participation from their Mailbox Provider.
Falk Informational PAGE 6
RFC 6449 CFBL Recommendations November 2011
o Full Body - An email message (the "DATA" portion of the [SMTP]
conversation) consists of two parts: the header and the body. The
"Full Body" is simply the entirety of the body of the message,
without modification or truncation. Note that images or other so-
called "attachments" are actually part of the body, designated in
accordance with the [MIME] standard.
o Full Header Section - An email message (the "DATA" portion of the
[SMTP] conversation) consists of two parts: the header and the
body. The header contains multiple header fields, each formatted
as "Header-Name: header contents". Although most Mail User Agents
(MUAs) only show the basic four header fields (From, To, Date, and
Subject), every message includes additional header fields that
primarily contain diagnostic information or data intended to
assist automatic processing. Often informally called "Full
Headers". These fields are fully defined in [RFC 5322]
o Header - See "Full Header Section" above.
o ISP - Internet Service Provider, usually referred to as either an
Access Provider or a Mailbox Provider in this paper.
o Mail Abuse Reporting Format (MARF) - See "Abuse Reporting Format"
above.
o Mailbox Provider - A company or organization that provides email
mailbox hosting services for End Users and/or organizations. Many
Mailbox Providers are also Access Providers.
o Mailing List - A set of Email Addresses that will receive specific
messages in accordance with the policies of that particular list.
o Message-ID Header Field - One of the diagnostic header fields
included in every email message (see "Full Header Section" above)
is the Message-ID. Theoretically, it is a unique identifier for
that individual message.
o Message Delivery - The process of transferring a message from one
mail transfer agent (MTA) to another. Once the message has been
accepted by the MTA operating on behalf of the Recipient, it is
considered to be "delivered" regardless of further processing or
filtering that may take place after that point.
o Message Originator - The Sender, but not necessarily the author or
creator, of a message.
o Message Recipient - The person or mailbox that receives a message
as final point of delivery.
Falk Informational PAGE 7
RFC 6449 CFBL Recommendations November 2011
o MIME - Multipurpose Internet Mail Extensions refers to a set of
standards permitting non-plaintext data to be embedded in the body
of a message. Concepts such as file attachments and formatted or
"rich" text are all accomplished solely through [MIME].
o MUA - Mail User Agent; loosely referring to the software used by
an End User to access, interact with, or send email messages.
o Provider - See "Feedback Provider" above.
o Received Header Field - Diagnostic header fields included in an
email message (see "Full Header Section" above) that start with
"Received:" and document (from bottom to top) the path a message
traversed from the originator to its current position.
o Recipient - See "Message Recipient" above.
o Return-Path - An optional message header field (see "Full Header
Section" above) that indicates the Envelope Sender of the message.
o Reverse DNS - The [DNS] name of an IP address, called "reverse"
because it is the inverse of the more user-visible query that
returns the IP address of a DNS name. Further, a Reverse DNS
query returns a PTR record rather than an A record.
o Sender - see "Message Originator" above.
o SMTP - Simple Mail Transfer Protocol, the mechanism and language
for transferring an email message from one place to another as
defined in RFC 5321 [SMTP].
o Spam - For the purposes of this document (and for most Complaint
Feedback Loops), "spam" is defined as any message that the
Recipient chooses to complain about, regardless of the intent of
the message's author or Sender.
o Spam Complaint - See "Complaint" above.
o Spammer - An entity that knowingly, intentionally sends Spam
messages (see "Spam" above).
o Terms of Use - A legal document describing how a particular system
or service is to be used.
o VERP - Variable Envelope Return Path [VERP], an informally
standardized method for encoding information about the Message
Recipient into the return path while delivering a message in order
to ensure that any non-delivery notices are processed correctly.
Falk Informational PAGE 8
RFC 6449 CFBL Recommendations November 2011
3. Mailbox Providers and Feedback Providers
In practice, a Mailbox Provider receives complaints from their End
Users, and is often also the Feedback Provider for those complaints
and is a consumer of feedback from other providers. In this
document, we separate the Mailbox Provider and Feedback Provider
functions to reduce possible confusion over those cases where they
are separate, and we also urge Mailbox Providers to read the
"Feedback Consumer" section later in this document.
3.1. Benefits of Providing Feedback
The decision to provide a Complaint Feedback Loop service should not
be taken lightly. The benefits of a Feedback Loop are great, but
success depends on a sound plan, organized implementation, and
dedication to upkeep.
What are some benefits of providing feedback to fellow Mailbox
Providers and Access Providers? Primarily, other industry actors are
quickly alerted to Spam outbreaks on their networks.
End Users are becoming more aware of and comfortable with mechanisms
to report Spam, and a Feedback Loop does just what it implies; it
closes the loop. The End User's complaint makes its way back to the
Message Originator (not necessarily the message Sender, who may be a
Spammer), allowing the originator to take appropriate action. In
this process, the mail system operator is just a messenger, relieved
of the responsibility of reviewing and forwarding complaints
manually.
Further, because every complaint is sent immediately -- without any
review or analysis by the Feedback Provider -- the complaint is
received by the Feedback Consumer in near real time. If the Feedback
Consumer is paying attention to their Feedback Stream and taking
appropriate action on it, the receiving Mailbox Provider receives
less Spam, blocks less legitimate mail, and does not have to assign
staff to follow up with the originating network. If the Mailbox
Provider does not pay attention to its Feedback Stream, and does not
take appropriate action, the Feedback Provider may block or otherwise
filter the email from that Message Originator, considering the
Feedback Messages to be sufficient notice.
What are some benefits of providing Feedback Loops to bulk Feedback
Consumers? As Message Recipients become more aware of and
comfortable with Spam reporting mechanisms, they often prefer this
method over the often-confusing and inconsistent "unsubscribe" or
"opt-out" mechanisms provided by most legitimate Message Originators
or Senders.
Falk Informational PAGE 9
RFC 6449 CFBL Recommendations November 2011
End Users often do not remember what lists they signed up for or are
otherwise not confident in the established relationship they may have
with a message Sender. As such, they often choose to report messages
as Spam to their Mailbox Providers, considering that to be sufficient
notification of their desire not to receive such email in the future.
If the Message Originator is paying attention to and taking
appropriate action on their Feedback Stream, it will have a happier
set of Message Recipients and should receive fewer Spam Complaints
(assuming their opt-in processes are sound). If the Message
Originator is not paying attention to Feedback and not taking
appropriate action, the Mailbox Provider may consider the Feedback
Stream sufficient notice that messages from that originator may no
longer be accepted in the future.
3.2. Collecting Complaints
To produce Feedback Messages and to ensure they are useful, the
Feedback Provider needs to obtain near real-time complaints from the
Mailbox Provider's users. This is typically done by integrating the
feedback mechanism with the collection of Spam reports from its
users.
These reports are typically made using the "Report Spam" buttons
integrated into Webmail interfaces, or a proprietary desktop client
provided to users. Mailbox Providers may also look at deploying a
toolbar or MUA plug-in that provides a "Report Spam" button in the
MUA interface.
Usability studies with average users should be performed on all
interface changes before implementation. A "help" interface should
also be available to educate users about how the Spam button should
be used and what it does.
If the Mailbox Provider does not offer its customers a mail client
with this button, then the Feedback Provider's chances for providing
an effective Feedback Loop are slim. While it is possible for the
Mailbox Provider to instruct its customers to forward unwanted mail
to a central location and for the Mailbox Provider to explain how to
ensure the report includes headers and bodies, the success rate of
customers doing so tends to be low. Even those complaints that do
contain all required information might prove difficult to parse, as
variations in formatting and content types will lead to automated
tools being consistently updated with new logic blocks for each
variation that occurs.
Falk Informational PAGE 10
RFC 6449 CFBL Recommendations November 2011
3.3. Creating Reports
It is recommended that Feedback Messages be sent using the standard
Abuse Reporting Format, to facilitate uniformity and ease of
processing for all consumers of feedback. This will also enable the
Feedback Provider to extensively automate the processes of generating
and sending Feedback Messages and of analyzing complaint statistics.
This format is described further in Appendix 1.
Feedback Loops are usually (but not always) keyed to the "last hop"
IP address (i.e., the IP address that passed the unwanted message to
the Mailbox Provider's servers). Consequently, the Feedback Provider
must be able to process the header from each complaint to determine
the IP address for the complaint.
A Feedback Provider may wish to provide, as part of its Feedback
Loop, other information beyond Spam Complaints that Feedback
Consumers may find valuable. It might include summary delivery
statistics (volume, inbox delivery rate, Spam trap hits, etc.) or
other data that the Feedback Provider may deem pertinent to Feedback
Consumers.
Any mature Feedback Loop system will produce situations in which the
Feedback Consumer may have follow-up questions or have other
information to provide in regard to the feedback. Feedback Messages
should include contact information (typically an Email Address) for
the Feedback Consumer to use for such questions, and ideally the
contact Email Address will feed into a ticket system or other
automated tool used by the Mailbox Provider's postmaster and/or anti-
abuse staff for handling general email delivery issues.
3.4. Policy Concerns
3.4.1. Privacy and Regulatory Compliance
Feedback Messages provide information relayed by Feedback Providers
from a Mailbox Provider's End Users to the Feedback Consumer. There
might not be any concerns with relaying non-private data to a third
party. However, the information provided in the complaints generated
by the user must be evaluated and any data deemed private may need to
be removed before distributing to a third party, per local policy.
For example, the Recipient's or reporter's Email Address and IP
address may be categorized as private data and removed from the
feedback report that is provided to the Feedback Consumer. Privacy
laws and corporate data classification standards should be consulted
when determining what information should be considered private.
Falk Informational PAGE 11
RFC 6449 CFBL Recommendations November 2011
Information provided by the Feedback Consumer to the Feedback
Provider for the purpose of enrolling in the Feedback Loop should
also be kept private. It should only be shared or used for the
purposes explicitly agreed to during the enrollment process (see the
"Terms of Use" section below).
Feedback Loops inevitably span country borders. Local laws and
regulations regarding distribution of information domestically and
internationally need to be considered when implementing a Feedback
Loop program. For example, in some European countries, data exchange
requires permission from governing bodies. The terms and
circumstances surrounding the exchange of data need to be clearly
defined and approved.
3.4.2. Terms of Use
A written Terms of Use agreement should be provided by the Feedback
Provider and agreed to by the Feedback Consumer before any feedback
is provided. The following concepts should be considered when
drafting the terms of use agreement:
o Data provided in Feedback Messages are provided to a specific,
approved entity. Information should not be transmitted outside of
the intended, approved Recipient. Any inappropriate use of the
information can lead to immediate termination from the feedback
program.
o Consumers of Feedback have a responsibility to keep the
information they provide for Feedback Loop purposes -- such as
abuse contact information, IP addresses, and other records --
accurate and up to date.
o The providing of Feedback information is a privilege and needs to
be treated appropriately. It does not entitle the consumer of the
feedback to any special sending privileges.
o Approval and continued enrollment in the program is a privilege
that can be denied or revoked for any reason and at any time.
3.5. Handling Requests to Receive Feedback
There should be a streamlined application process for receiving
feedback and the vetting of such applications. This vetting may be
stringent in cases where the Mailbox Provider chooses to tie its
Complaint Feedback Loop program to a whitelist. Criteria may involve
the following:
Falk Informational PAGE 12
RFC 6449 CFBL Recommendations November 2011
o Cross-checking that the requestor is indeed authorized to receive
feedback for the IP addresses concerned.
o Gathering other information such as whether the IPs are an ISP
smarthost network, a webhosting farm, an email marketing or
Mailing List service, or other entity.
o Requesting information such as a link to the policies of the
requestor, contacts to send Feedback Messages, and escalation
points of contact.
Ideally, enrollment will be a two-step process, with the applicant
filling out a form and being required to receive and acknowledge a
confirmation email (best sent to abuse@ or postmaster@ the domain in
question) before the applicant's request is even put into the queue
for the Feedback Provider to process.
Ownership of IP addresses can and should be cross-checked by means of
origin Autonomous System Number (ASN), WHOIS/RWHOIS records, Reverse
DNS of the sending hosts, and other sources. This can be automated
to some extent, but it often requires some manual processing.
3.5.1. Application Web Site
Applications for Feedback Loops can be accepted on a stand-alone web
site or can be part of the Mailbox Provider's postmaster site.
Regardless, the web site for the Complaint Feedback Loop program
should contain other content specific to the Feedback Loop, including
FAQs for the Feedback Loop program, the Terms of Service for the
Feedback Loop, and perhaps a method for enrolled parties to modify
their existing enrollments.
The web site should also provide the Feedback Consumer with general
information on how the feedback will be sent, including:
o Report Format (ARF or otherwise)
o Sending IP addresses and/or DKIM "d=" string
o "From" Email Address
Falk Informational PAGE 13
RFC 6449 CFBL Recommendations November 2011
3.5.2. Saying No
Denial of a Feedback Loop application may be appropriate in certain
cases such as:
o Where the Feedback Provider suspects "gaming" of delivery policies
via the Feedback received, with attempts to pollute Feedback Loop
metrics by, for example, creating bogus accounts and reporting
false negatives with these, to offset the negative reputation
caused by high complaint rates.
o Where the Feedback Provider has decided to block the Message
Originator's IP space for which feedback has been requested on the
grounds that email from that originator has a sufficiently
negative reputation that it will not be delivered at all. This is
somewhat on the lines of a global unsubscribe of the Message
Provider's users from the originator's lists, which would make
rendering additional feedback unnecessary.
It is recommended that the Feedback Provider send notification if an
application is denied. Additionally, they should maintain a
documented, clear, and transparent appeals process for denial of
requests. This process can be as simple as the prospective Feedback
Consumer replying to the denial email requesting review or escalation
to a team lead, which also cites reasons the application should be
reviewed.
3.5.3. Automation
For a Feedback Loop to be cost-effective and usable for large
Feedback Consumers and Feedback Providers, it must be possible for
reports to be generated and processed automatically without any human
interaction. On the other hand, it should be possible for small
Feedback Consumers to handle a low volume of reports manually,
without requiring any automation.
In automating the feedback process, the consumer of the Feedback
Stream must receive enough information about the report that it can
take appropriate action, typically to remove the Recipient from the
Mailing List about which it is sending a report. The Recipient's
Email Address is not enough, as the Recipient may be on several
Mailing Lists managed by the Feedback Loop consumer and only need to
be removed from the particular list reported.
Also, some producers of Feedback Loops might redact the Recipient's
Email Address for privacy reasons. Effective implementation of a
Complaint Feedback Loop requires that the Feedback Provider put in
Falk Informational PAGE 14
RFC 6449 CFBL Recommendations November 2011
place as many automated processes and tools as feasible to handle all
aspects of the process. Feedback Providers should seek to automate
or script the following:
o Accepting and validating Feedback Loop Applications from
prospective Feedback Consumers.
o Processing requests to determine whether or not they meet the
Feedback Provider's criteria for enrollment in the program.
o Accepting Spam Complaints from End Users; this will form the bulk
(and perhaps sole) component of the feedback sent by the Feedback
Provider.
o Production of Feedback Messages from Spam Complaints.
o Production of other Feedback Loop artifacts as chosen by the
Feedback Provider.
o Optionally, provision of a mechanism for Feedback Consumers to
further engage a Feedback Provider about a given Feedback Message.
o Ongoing validation of Feedback Loop enrollments to determine if a
currently enrolled IP address or network merits continued
inclusion in the Feedback Loop.
o Optional periodic emails to Feedback Consumers to determine if
their enrolled Email Addresses are still valid.
3.6. Ongoing Maintenance
It is recommended that self-service maintenance be offered to
Feedback Consumers, to the extent practicable. The more they can do
themselves, the less you have to do.
3.6.1. IP Validation
The criteria that a Feedback Provider uses to validate a Feedback
Loop application may change over time. It is a near certainty at
least some subset of Feedback Consumers enrolled to receive feedback
will at some point after enrollment fail to meet those criteria,
regardless of whether or not the criteria change.
The Feedback Provider should put in place tools to periodically
re-validate all Feedback Consumers enrolled in its Feedback Loop
system against its current criteria. Additionally, the Feedback
Falk Informational PAGE 15
RFC 6449 CFBL Recommendations November 2011
Provider will likely have objective criteria for remaining in the
Feedback Loop for enrolled Feedback Consumers; the enrolled consumers
should be validated against those criteria as well.
3.6.2. Email Address Validation
Just as some Mailing List software has the built-in ability to send
periodic "probe" emails to subscribed addresses to validate them, so
too should the Feedback Provider develop tools to send similar emails
to the addresses receiving Feedback Messages to ensure that they are
valid. This is especially true for the addresses that are not the
abuse@ and postmaster@ addresses originally used as part of the
enrollment acknowledgment step. Over time, people may change
employers, or at least roles, and validating the Email Addresses
associated with an IP is one way for the Feedback Provider to ensure
that Feedback Messages are still being accepted and acted upon by the
Feedback Consumer.
3.6.3. Feedback Production Changes
Updating Feedback Consumers when one's own IP addresses are changing
is an important aspect of Feedback Loop maintenance. The exact
format, automation, and other considerations of these updates are
outside the scope of this document, but are topics worthy of further
discussion and eventual documentation.
4. Feedback Consumers
A Feedback Consumer receives its Feedback Messages after its
submitted Application for a Complaint Feedback Loop is approved. A
Feedback Consumer will usually have Complaint Feedback Loop
subscriptions set up with multiple Feedback Providers. Different
Feedback Streams may be in different formats or include different
information, and the Feedback Consumer should identify a process to
organize the data received and take appropriate action.
A Feedback Consumer, Mailbox Provider, or Access Provider (i.e., a
hosting company or ISP) will use this Feedback to identify network
compromises, fraudulent accounts, policy violations, and other
concerns. The Feedback Loop provides real-time visibility into Spam
Complaints from Message Recipients, greatly enabling these Mailbox
Providers to mitigate Spam propagating from their networks.
Senders of bulk email should use the complaints to make decisions
regarding future mailings. Such decisions may include one or more of
the following: modification of email frequency, branding, opt-in
practices, or list management.
Falk Informational PAGE 16
RFC 6449 CFBL Recommendations November 2011
The authors of this document urge those who are solely Feedback
Consumers to also read the previous sections for Mailbox Providers
and Feedback Providers. This will provide the proper context of the
recommendations included below.
Further recommendations for bulk senders may be found in the MAAWG
Sender Best Communications Practices [MAAWG-BCP].
4.1. Preparation
Feedback Consumers need to prepare to process and act on feedback
before asking to receive it. At a minimum, make sure to have:
1. The "Role" Email Addresses such as abuse@ and postmaster@. The
person who applies for the Feedback needs to make sure they have
access to these Email Addresses. Feedback Providers often send a
confirmation link to those accounts to prevent End Users,
Spammers, or competitors from signing up for Feedback for which
they are not authorized.
2. A dedicated Email Address to receive the Feedback Messages, such
as fbl@example.com or isp-feedback@example.com. While not
required, this will make it easier for to process the reports
received.
3. A list of IP addresses for which you want to receive Feedback
Messages, making sure you can prove the ownership of the IP
addresses and associated domains. Feedback Providers often
require that:
* Reverse DNS for each IP shares the domain of either the
applicant's Email Address or the Email Address that will be
receiving the Feedback Messages.
* WHOIS information for the IPs requested is obviously
associated with the domain name.
4. Contact information such as name, Email Address, phone number,
and other relevant information.
5. The knowledge that if the application form asks for your credit
card number or other financial information, it is assuredly a
scam.
Falk Informational PAGE 17
RFC 6449 CFBL Recommendations November 2011
4.2. What You'll Receive
Once a Feedback Consumer has signed up to receive feedback from a
Feedback Provider, it may also receive several other sorts of
delivery-related reports. This includes Feedback Messages,
administrative messages, and other messages.
4.2.1. Feedback Reports
Feedback Messages are the main emails generally associated with a
Feedback Loop. Each time a Recipient hits the "This Is Spam" button,
the Feedback Loop system creates a boilerplate report with a copy of
the original email attached and sends it to the consumer of the
Feedback Loop.
The handling of feedback reports is discussed in the next section.
4.2.2. Administrative Messages
Administrative messages will typically be sent to the Email Address
provided for contacting the person who originally applied for the
Feedback Loop, rather than to the address provided for handling the
Feedback Messages. These messages are likely to be sent infrequently
and irregularly, but it is important they are seen by the person
managing the Feedback Stream processor in a timely manner. It is
usually a poor idea to have these sent to an individual's Email
Address since they may be lost if that person is on vacation, changes
position within the company, or leaves the company.
Instead, they should be sent to a role account that goes to a
ticketing system or "exploded" to multiple responsible parties within
the organization. If there is not already an appropriate role
account such as support@ or noc@ that reaches the right team, it may
be a good idea to set up a dedicated alias such as fblmaster@ to sign
up for all Feedback Loops.
4.2.3. Report Cards
The detail in a report card can vary greatly. Feedback Providers
might send a regular summary of traffic levels and complaint rates
seen, perhaps just an overview or possibly broken down by source IP
address or some other identifier. Sometimes these may be sent just
when some metric (typically a complaint rate) reaches a level that
causes the Mailbox Provider to notify the Feedback Consumer there may
be a problem developing that needs to be investigated and addressed.
At the other extreme, some report cards will contain almost no useful
Falk Informational PAGE 18
RFC 6449 CFBL Recommendations November 2011
data at all, just a warning that the Message Originator is causing
complaints -- with the implication that its email will be blocked
unless it is improved.
Report cards are human readable, since there are not currently any
standard machine-readable formats and the information they include,
both the provided metrics and their semantics, varies widely from one
Mailbox Provider to another. They are useful reference overviews for
a Message Originator to monitor the overall perceived quality of the
email it sends and, in the case of ESPs, perhaps which customers are
causing higher than expected rates of complaints. They can also be
the only warning of serious problems prior to email being blocked
altogether by the receiving Mailbox Provider. It is critical they be
are seen by someone handling delivery issues for the Message
Originator, so again, they should be handled by an email alias that
is always read.
Report cards also contain useful data to track mechanically and
perhaps report on trends, though as their content varies, it is hard
to generalize what use might be made of them. At the very least, the
"warning" report cards are something that should be visible on an
ESP's business intelligence or delivery dashboard.
4.3. Handling Feedback Messages
Mailbox Providers sending feedback may have published policies as to
how they expect a Feedback Consumer to use Feedback Messages or may
expect the Feedback Consumer to simply "make the problem stop". In
practice, this mostly boils down to three things:
o First, where the consumer of the feedback has some specific
control over sending the email, it is expected not to send email
of the same type to the same Recipient again.
o Second, it should identify the underlying problem (if any) and fix
it so that it receives fewer reports of that type in the future.
o Third, it is not necessary to inform the Mailbox Provider or
Feedback Provider, or their End User(s), of which actions have
been or will be taken in response to automated complaint feedback.
If the Feedback Consumer is a separate entity from the Message
Originator, the two entities are expected to work together to resolve
any problem.
Falk Informational PAGE 19
RFC 6449 CFBL Recommendations November 2011
4.3.1. Unsubscription or Suppression
A Sender (whether author or originator) of commercial email should
treat the Feedback Message similar to an unsubscribe request,
ensuring that no further email from that list is sent to that
Recipient, either by removing the email from that list or adding it
to the associated suppression list. It needs to use its best
judgment, keeping in mind the goal of reducing future complaints, as
to how broadly to apply that unsubscribe. Suppressing the address
across an entire ESP is likely too broad. However, if a single
Feedback Consumer (or customer of an ESP) has multiple segmented
lists, then suppressing them across all those lists is probably a
good idea.
It is universally acknowledged that not all complaints are
intentional; for example, Recipients might accidentally hit the wrong
button or mark an entire mailbox as Spam. However, it is best for
Feedback Consumers to assume the Recipient does not want more email
and to suppress mail to the Recipient in all but fairly extreme cases
such as a Mailing List the Recipients pay to receive, email from a
genuine company to its valid employees, or email from an Access
Provider or Mailbox Provider to its users.
This gets more complex in the case of transactional mail -- mail that
is tied to some other service, such as ticket purchase confirmations
or billing statements. In that case, the Feedback Consumer has to,
again, use its best judgment based on the specific situation. In
some cases, the right thing to do may be to communicate with the
Recipient via another channel, such as a message on a web site used
for the service; i.e., "You reported your notification mail as Spam
so we are not going to send you any more messages unless you tell us
otherwise".
In some cases, the best thing to do may be to ignore the Feedback
Message. For example, if your customer has reported as Spam the
airline tickets he purchased and you emailed him, he probably did not
mean it and he is going to be very annoyed if you do not send him the
other tickets he has ordered. In rare cases, it might be appropriate
to suppress email to the Recipient, but also to suspend access to a
service he or she uses until the Recipient confirms a desire to
receive the associated email. In all these cases, the important goal
is to keep the customer happy and reduce future complaints, even in
the apparently paradoxical situations where the way to do that is to
ignore their Feedback. In the real world, however, these are a small
minority of cases.
Falk Informational PAGE 20
RFC 6449 CFBL Recommendations November 2011
4.3.2. Trending and Reporting
Counting the Feedback Messages received over regular time periods can
provide much useful information to ISPs, ESPs, and other Feedback
Consumers, especially when broken down appropriately.
An ISP (Mailbox Provider or Access Provider) might want to count the
number of Feedback Messages a particular customer or IP address
causes in a given day. If there is a sudden increase from a
particular customer or server, it may be a sign that a Spammer has
signed up or a system has been compromised. If there is a high level
of complaints about a particular customer, it may be worth
investigating to see if there is a reason for that. For example, 10
Feedback Messages a day would be a sign of serious problems in some
cases, but might be perfectly reasonable "background" levels for a
Message Originator that sends 300,000 emails a month. If the count
shows there may be a problem, the ISP can dig down and look at the
emails that are being reported to determine the underlying cause.
An ESP can do similar things but can also break the data down in more
ways: by customer, by Mailing List, by campaign. An ESP also has
access to more information; it knows how many emails were delivered
to the receiving Mailbox Provider over a given time period. As a
result, it can estimate the number of complaints divided by the
number of emails sent, which is often a more useful metric than the
absolute number of reports. This is critical data for ESPs to track
over time because it can help identify and quantify problem
customers.
An individual Feedback Consumer, whether sending their own email or
using an ESP, can acquire at least some information from complaint
rates. A spike in complaints on an otherwise stable list might be a
sign there is a problem with address acquisition, if the spike is due
to reports from new subscribers. If it came from older subscribers,
it might be attributable to content of a particular mailing that was
not well received. Perhaps the branding was not recognized or the
content was offensive or inappropriate for the list.
The complaint rate is determined by the number of Feedback Messages
received over a given time period divided by the number of emails
delivered to the associated Mailbox Provider over the same period.
It is an obvious and useful metric to track, but there are a few
subtle issues to be aware of.
One issue is that Feedback Messages tend to be counted on the day the
complaint was sent, which is the day the original message was read by
the Recipient. That may not be the same day that the message was
sent. A simple example is the fact that a Message Originator that
Falk Informational PAGE 21
RFC 6449 CFBL Recommendations November 2011
sends email regularly Monday through Friday will often see a high
complaint rate on Saturday. The absolute number of Feedback Messages
sent by people catching up with the week's email over the weekend may
not be that high. However, since hardly any email is sent on
Saturday, a fairly reasonable number of complaints end up being
divided by a very small number of total sent emails, possibly even
zero, which would break the reporting engine. This can lead to a
complaint rate that seems to range anywhere from suspicious to
ridiculous. Consequently, large Mailing Lists that are virtually
silent on the weekend could end up receiving more complaints on a
Saturday than email they sent that day, leading to complaint rates of
well over 100%.
Another arithmetic issue to consider is the interaction between the
inbox, the bulk folder, and the "This Is Spam" button. If an
organization sends a high volume of email that has a terrible
reputation, it may end up with perhaps 500 of its 10,000 mails in the
inbox and the remaining 9,500 in the bulk folder. If it gets 10
Feedback Messages and divides that by the 10,000 emails it sent, it
will get a very respectable 0.1% complaint rate. However, the
Mailbox Provider is probably going to calculate the complaint rate by
dividing the number of emails delivered to the inbox instead --
giving a 2% complaint rate, which is probably grounds for immediate
blocking. So, if one sees a large difference between a complaint
rate as reported by a Mailbox Provider or other reputation system and
the rate calculated from raw delivery numbers, it is important to
look closely at the data.
4.4. Automatically Handling an Incoming Feedback Stream
Even when signing up for a Feedback Loop is partly automated,
modifications to it tend to be handled manually. Even something as
trivial as changing the Email Address that the Feedback Messages are
sent to can be time-consuming and can cause significant overhead to
the Feedback Provider. Multiply that by a dozen Feedback Loops, and
getting it right the first time can save a lot of time and energy.
Even the smallest of users should create a unique email alias for
each Feedback Loop. There are several advantages to this, even if
they all deliver to the same person's inbox at first. Sending each
Feedback Loop to a unique address makes it immediately clear which
Feedback Provider was the source of any given report, even if it is
sent from an inconsistent From address. It makes it easy to put
lightweight pre-processing in place for a particular Feedback Stream,
if needed. It makes it easy to discard Feedback Messages if needed
(though only temporarily, as it could be very bad for one's
Falk Informational PAGE 22
RFC 6449 CFBL Recommendations November 2011
reputation to miss a changing trend). If a Feedback Consumer needs
to scale up, it is easy to point the existing aliases at a Feedback
Loop processing engine.
If an organization might possibly scale up appreciably in the future
or consider outsourcing its Feedback Loop processing to a third-party
Feedback Consumer, it may be even better to create a subdomain for
handling Feedback Streams. For example, example.com might use
fbl-aol@fbl.example.com to accept its AOL Feedback Loop, allowing it
to delegate the whole of @fbl.example.com to a Feedback Loop handling
appliance or service, should the need arise.
Small Feedback Consumers, with lists of no more than a few thousand
Recipients, or small ISPs with no particular history of problems,
should be able to handle feedback reports with little or no
automation, as an ARF message should be readable in most mail
clients. It may be worthwhile to add some very lightweight
processing to the inbound Feedback Messages to make them easier to
triage from other email client. For example, arffilter.c [Wise] can
annotate the Subject line of inbound Feedback Messages with the IP
address being reported, making it easier to see patterns of problems
by sorting the messages by Subject line in the mail client. To
identify which Recipient is causing the feedback to be sent, small
Feedback Consumers should add some of the automation mentioned below
that is intended for larger Feedback Consumers.
Larger Feedback Consumers need to be able to automate the handling of
Feedback, as it scales beyond the ability of someone to manage
manually quite quickly. The main capability a Feedback Loop
processor needs is to extract some relevant data from the report,
reliably. The most important bits of data tend to be the following:
o The Recipient of the original email
o The Mailbox Provider originating sending the Feedback Message
(some Feedback Providers operate on behalf of multiple Mailbox
Providers)
o The customer who sent the original email (in the case of an ESP or
Mailbox Provider)
o The campaign and Mailing List that the original email belonged to,
if any
o (Possibly) the IP address from which the original email was sent
and any [DKIM] signature domain
Falk Informational PAGE 23
RFC 6449 CFBL Recommendations November 2011
The last isn't vital, but may be a useful piece of data in diagnosing
delivery problems.
It can be very difficult to extract some of this data without some
upfront work before email is sent. Some Feedback Providers will
redact the Email Address in the To: header or Recipient Email
Addresses anywhere within the message. Some will delete any
identifying information they can. It may be possible to identify the
End User based on the Message-ID, Subject line, and Received header
timestamps, if there is access to the mail server logs, but at best
it is painful and time-consuming, and only worth doing in an
exceptional case.
The solution is similar to the one used for automated bounce handling
using VERP -- embed the information in the email in a way that it is
unlikely to be removed by Feedback Providers but is easy to recognize
in the email. That information may already be there in a form such
as VERP if the Return-Path header is included in the embedded email,
or included in one-click unsubscribe links included in the body of
the email. If it is not already there, a good place to add the
information is in the local part of the Message-ID as that is often
used to track the progress of email through delivery. It is often
available from log files as well as in the headers of the original
message included in the Feedback Message.
There are several good ways to store the mapping between Recipients
and identifiers in mail. For a database-backed ESP or bulk sender, a
synthesized database primary key can be used. It is very small, and
very opaque, and it is not expensive to retrieve the associated data
from the main database -- but it is impossible to read by hand.
Therefore, it needs automation with access to the core database to
map the key onto the actual data.
Recording the required information directly within the email but
encrypting it with strong or weak encryption removes the need for
database access to extract the data. However, it still does need
some automation.
A hybrid approach with the various bits of data stored separately but
having some pieces either encrypted or obfuscated is possible by just
including a database ID. This can provide a good compromise where
most of the data is not immediately obvious to third parties but
patterns in it can be recognized by eye. For example, a Message-ID
of "esp-423-27-42460@example.com" is opaque to a third party, but
someone familiar with the format can tell that it is a Message-ID
added by the system. In this case it starts with "esp" followed by
three numbers separated by dashes, meaning it is from customer 423,
campaign 27, and the Recipient has the database key 42460. Even
Falk Informational PAGE 24
RFC 6449 CFBL Recommendations November 2011
decoding this manually, while it may not be possible to identify
customer number 423, it is easy to recognize that 10 Feedback
Messages in a row relate to the same customer. From experience, it
is not unusual for the vast majority of reports at an ESP to be about
a very small number of customers, and one learns their customer IDs
very quickly.
Once a Message Originator embeds Recipient identifiers in an easily
recognizable format in all its mail, it is quite easy for a Feedback
Message processor to extract that with a conventional expression
match and possibly a couple of database queries. It can then
suppress that Email Address and record the customer and campaign for
future reporting. In the case where the Feedback Messages are
recorded in a ticketing system, it can also annotate the tickets with
that data (again, for reporting and trending analysis).
A Feedback Message processor is often bolted onto the side of an
already complex bulk mail generator, making it difficult to reliably
suppress mail to the Recipient. If the delivery data is stored in a
way that makes it easy to convert into the same format as the VERP
string used for bounce processing then the Feedback processor can
create a "fake" hard bounce and send it to the existing bounce
processor, suppressing mail to that address.
Mailbox Providers and Access Providers also need to automate Feedback
processing. They are usually less interested in the details about
the message and more interested in the IP address and which customer
sent it. In most cases, the IP address can be extracted easily from
ARF metadata; whereas, in other cases, it may need to be extracted
from the Received headers embedded in the included original message.
That data can then be used both for automated forwarding of Feedback
Messages to the originating customer, if the ISP feels that is
appropriate, and also for reporting on complaint levels across the
ISP's customer base.
5. Conclusion
Whether you are acting as a Mailbox Provider or a Feedback Consumer,
Complaint Feedback processing can be complex and scary -- or, with
some intelligence and automation, simple and easy. In either case,
it is an important and necessary tool for detecting messaging abuse
and ensuring End User satisfaction.
MAAWG encourages all Mailbox Providers to offer Feedback of whatever
form is appropriate for their local user base and legal framework,
and it encourages all Senders of email to consume and act upon any
Feedback available. An actively maintained list of known Feedback
Loops can be found at [Wise].
Falk Informational PAGE 25
RFC 6449 CFBL Recommendations November 2011
6. Acknowledgments
This document was written within the MAAWG Collaboration Committee.
The project was led by John Feaver and Kate Nowrouzi. The primary
authors were Steve Atkins, Christine Murphy Borgia, J.D. Falk, John
Feaver, Todd Herr, John Levine, Heather Lord, Kate Nowrouzi, and
Suresh Ramasubramanian.
The document was edited by John Levine, J.D. Falk, and Linda Marcus.
Further editing and formatting required for this version to be
published by the IETF was performed by J.D. Falk, with advice from
Barry Leiba and Murray Kucherawy.
6.1. About MAAWG
[MAAWG] is the largest global industry association working against
Spam, viruses, denial-of-service attacks, and other online
exploitation. Its members include ISPs, network and mobile
operators, key technology providers, and volume sender organizations.
It represents over one billion mailboxes worldwide, and its
membership contributed their expertise in developing this description
of current Feedback Loop practices.
7. Security Considerations
Security and privacy considerations are discussed in many sections of
this document, most notably Sections 1, 3.4, and 3.5.
8. Informative References
[DKIM] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys
Identified Mail (DKIM) Signatures", RFC 6376,
September 2011.
[DNS] Mockapetris, P., "Domain names - concepts and
facilities", STD 13, RFC 1034, November 1987.
[DomainKeys] Delany, M., "Domain-Based Email Authentication Using
Public Keys Advertised in the DNS (DomainKeys)",
RFC 4870, May 2007.
[MAAWG] Messaging Anit-Abuse Working Group,
<http://www.maawg.org/>.
Falk Informational PAGE 26
RFC 6449 CFBL Recommendations November 2011
[MAAWG-BCP] MAAWG, "MAAWG Sender Best Communications Practices
Executive Summary and MAAWG Sender Best Communications
Practices Version 2.0a-Updated", September 2011,
<http://www.maawg.org/sites/maawg/files/news/
MAAWG_Senders_BCP_Ver2.pdf>.
[MARF] Shafranovich, Y., Levine, J., and M. Kucherawy, "An
Extensible Format for Email Feedback Reports",
RFC 5965, August 2010.
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996.
[RFC 5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
[RFC 5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
July 2009.
[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[Trust] Crocker, D., Ed., "Trust in Email Begins with
Authentication", Issued by the Messaging Anti-Abuse
Working Group (MAAWG), June 2008,
<http://www.maawg.org/sites/maawg/files/news/
MAAWG_Email_Authentication_Paper_2008-07.pdf>.
[VERP] Wikipedia, "Variable Envelope Return Path",
<https://secure.wikimedia.org/wikipedia/en/wiki/
Variable_envelope_return_path>.
[Wise] "arffilter - rewrite ARF reports",
<http://wordtothewise.com/products/arffilter.html>.
Falk Informational PAGE 27
RFC 6449 CFBL Recommendations November 2011
Appendix A. Abuse Reporting Format (ARF)
A.1. A Brief History
The approach used by the first Feedback Loop to be deployed -- the
"scomp" system at AOL -- was to send an entire copy of the message to
the consumer of the Feedback Loop. It expected that large Feedback
Consumers would embed sufficient information in the email so they
could identify which Message Recipient had complained.
That worked well enough when there was only a single entity providing
feedback, but as other Mailbox Providers started to offer Feedback,
it became clear that it would be useful for the Feedback Provider to
be able to add some additional information, both machine readable and
human readable, to the report. This led to ARF, the Abuse Reporting
Format, which quickly became the de facto standard for Feedback
Messages.
Today, ARF is used by nearly all Feedback Providers, both within
MAAWG and without, constituting the vast majority of all Feedback
Messages generated worldwide. ARF is recognized by all MAAWG members
that have developed software or services that consume and process
Feedback Messages. There are no competing standards for reporting
individual messages.
ARF has now been published by the IETF as RFC 5965 [MARF].
A.2. Structure of an ARF Message
An ARF report (Feedback Message) is sent by email, with one message
sent for each Spam report made. It consists of three sections, in a
standard [MIME] message format called multipart/report.
The first section contains human-readable plaintext, primarily for
the benefit of small Feedback Consumers who are handling reports
manually. It typically contains boilerplate text explaining that
this is a Feedback Message and providing URLs to other data such as
contact information for the Feedback Provider or Mailbox Provider
that originated the Feedback Message.
The second section contains some machine-readable information,
including the version of the ARF protocol used and the type of report
it is ("abuse," "fraud," or other label). It also might include some
optional information about the email being reported, such as the
original Envelope Sender or the time the mail was received. In
theory, the information in this section can be used to mechanically
route and triage the report, though in current practice most Feedback
Falk Informational PAGE 28
RFC 6449 CFBL Recommendations November 2011
Messages are treated identically. As a result, this section is often
ignored entirely by Feedback Consumers who prefer to process the
third section themselves.
The third section of the report consists of a copy of the original
email that the report is about, as a standard [MIME] message/RFC 822
attachment. While ideally this would be an unmodified copy of the
original email, it is likely that many producers of reports will
modify or "redact" some elements of the report, especially the Email
Address of the Recipient, due to privacy or other legal concerns.
The strict technical specifications of ARF, as well as some example
reports and tools to handle the format, can be found at
<http://mipassoc.org/arf/>, [Wise], and in [MARF]
Appendix B. Using DKIM to Route Feedback
Historically, the IP address of the "last hop" -- the MTA that
transferred a message into the receiving Mailbox Provider's
administrative domain -- was the sole reliable identifier used to
denote the source of a message. With the emergence of authentication
technologies such as [DKIM], another identifier can now be used;
specifically, the authenticated domain associated with a message.
This domain is the "d=" value in a DKIM-Signature header field.
In a social or policy context, applying a DKIM signature to a message
is tantamount to stating, "I take responsibility for this message".
The DKIM signature is most often applied by the author or originator
of a message, which may be far upstream of the "last hop" MTA. This
is true particularly in cases where the originator's intended
Recipient Email Address is configured to forward to another Recipient
Email Address. Stories of users who have strung together multiple
forwarding accounts are not uncommon, and these users are unable to
complain effectively about Spam because their Mailbox Providers
cannot easily or reliably follow the path of a message back to the
initial originator.
A single DKIM "d=" value may be used across multiple servers with
multiple IP addresses. Servers may be added or removed at any time
without changing the dynamics of the DKIM signature. When a Feedback
Loop is based on the IP address, the Feedback Consumer must contact
the Feedback Provider to change its subscription options every time
an IP address needs to be added or removed. However, when a Feedback
Loop uses DKIM, no reconfiguration is necessary because the signing
domain does not change.
Falk Informational PAGE 29
RFC 6449 CFBL Recommendations November 2011
One recurring concern with DKIM, however, is that ESPs often send
messages addressed with hundreds or thousands of customer domains,
yet they want to receive Feedback Messages for all of these domains.
This was particularly difficult with [DomainKeys] (the predecessor to
DKIM), which tied the "d=" to the "From" header field. DKIM removed
this tie, so it is simple for an ESP to use a domain of its own to
sign the message and sign up for Feedback regarding all messages
signed with that domain. Such a signature may be in addition to, or
instead of, signatures from the various client domains. While there
are still many unknowns related to reputation (which will be
addressed in a future MAAWG document), this is clearly an appropriate
use of DKIM to take responsibility (and receive Feedback) for a
message.
Appendix C. Unsolicited Feedback
Is it always necessary for a Feedback Consumer to apply for a
Feedback Loop or is it permissible for a Feedback Provider to
configure a Feedback Loop for a Feedback Consumer without an explicit
request? There is continuing debate about whether this is an
acceptable practice, and MAAWG is neither endorsing nor condemning
such activity at this time.
That said, if a Feedback Provider chooses to send Feedback without
being asked first, certain guidelines should be followed. In
general, it should make prudent decisions to minimize the negative
impact on Mailbox Providers and Access Providers.
C.1. Guidelines
This should only be done for Mailbox and Access Providers.
This should only be done after attempting to contact the provider to
ask if it is possible to set up a Feedback Loop via the normal
practice.
These Feedback Loops should only be set up to send to the published
abuse address from the provider's WHOIS record.
C.2. Pros
Feedback Consumers may not realize they have abuse problems until
they begin receiving the spam complaints.
Feedback Consumers may not be aware of Feedback Loops and may
appreciate the additional data feed.
Falk Informational PAGE 30
RFC 6449 CFBL Recommendations November 2011
Upstream providers have an additional information stream to help them
identify problem customers.
Spam coming from a network is abuse; therefore it is appropriate to
send reports of the abuse back to the Mailbox Provider or Access
Provider. Setting up a Feedback Loop automates the process.
C.3. Cons
It creates confusion for Feedback Consumers if they did not apply and
do not understand why they are suddenly receiving complaints.
It can conflict with existing Terms of Service because a new feed of
information is available. For example, if a provider has a policy to
terminate service after a certain number of abuse complaints, and it
starts receiving unexpected Feedback Loop complaints, it may either
be forced to terminate customers that did not have a previous issue
or be required to update its Terms of Service and Acceptable Use
Policy agreements.
Upstream providers do not have access to the mail being sent by their
customers, so they cannot tell whether bulk mail complaints
constitute a problem.
The listed abuse address may not be the correct place for automated
spam complaints to be sent.
The listed abuse address may feed into a ticketing system that is not
capable of correctly handling ARF messages.
Feedback Consumers may not be equipped to handle the volume or format
of complaints without some warning and preparation.
Author's Address
J.D. Falk (editor)
Messaging Anti-Abuse Working Group
Presidio of San Francisco
P.O. Box 29920
572 B Ruger Street
San Francisco, CA 94129-0920
US
EMail: ietf@cybernothing.org
URI: http://www.maawg.org/
Falk Informational PAGE 31
RFC TOTAL SIZE: 75139 bytes
PUBLICATION DATE: Thursday, November 17th, 2011
LEGAL RIGHTS: The IETF Trust (see BCP 78)
|
