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Internet Engineering Task Force                                  T. Zink
Internet-Draft                                                 Microsoft
Intended status: Informational                              May 11, 2012
Expires: November 15, 2012

     Recommendations for the use of whitelists for email senders
                  transmitting email over IPv6


   This document contains a plan for how providers of email services
   can manage the problem of email abuse over IPv6. Spammers can
   send mail from a very large range of IPv6 addresses, and this will
   make current antispam technology less effective.  This is because
   email receivers will have to maintain excessively large lists
   of IP blocklists which either consume too many resources, or will
   become stale and therefore ineffective as spammers quickly
   discard one IP and move onto the next one.  This document recommends
   that during the interim  transition of email from IPv4 to IPv6,
   email receivers implement a whitelisting option where they only
   allow email from permitted senders over IPv6 and reject mail
   from everyone else sending email over IPv6.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 15, 2012.

Copyright Notice

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   This document may contain material from IETF Documents or IETF
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Table of Contents

   1.  Key Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction and Problem Statement . . . . . . . . . . . . . .  5
   3.  Important Notice of Limitations and Scope  . . . . . . . . . .  5
   4.  Transition Model - Whitelists  . . . . . . . . . . . . . . . .  6
   5.  Population of the IPv6 Whitelists  . . . . . . . . . . . . . .  7
   6.  Privacy Considerations . . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   Appendix A.  Document Change Log . . . . . . . . . . . . . . . . .  9
   Appendix B.  Open Issues . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

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1.  Key Terminology

   This section defines the key terms used in this document.

1.1.  Email

   Email is a method of exchanging digital messages from an author to
   one or more recipients.

1.2.  Web mail

   A service which offers web based access to email services which would
   otherwise be accessed by dedicated email programs running on the
   device used to access the email.

1.3.  Host

   An end user's host, or computer, as used in the context of this
   document, is intended to refer to a computing device that connects to
   the Internet.  This encompasses devices used by Internet users such
   as personal computers, including laptops, desktops, and netbooks, as
   well as mobile phones, smart phones, home gateway devices, and other
   end user computing devices which are connected or can connect to the
   public Internet and/or private IP networks.

   Increasingly, other household systems and devices contain embedded
   hosts which are connected to or can connect to the public Internet
   and/or private IP networks.  However, these devices may not be under
   interactive control of the Internet user, such as may be the case
   with various smart home and smart grid devices.

1.4.  SMTP

   As defined in RFC5321

1.5.  Internet Customer

   An end user who leverages a connection to the Internet via an ISP and
   is provisioned with a public IP to communicate on the Internet.

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1.6.  Internet facing server

   A server which is addressed with a public IP address that is able to
   communicate with other publically addressed servers.  A server
   typically hosts a service that can be utilized by the Internet

1.7.  Internal users

   Known corporate users of the ISP entity.

1.8.  Blocklist

   A list of IP addresses that are known to send spam.  Email filters
   typically reject mail from IPs on blocklists.  Blocklists are also
   known as blacklists.

2.  Introduction and Problem Statement

   With the depletion of IPv4 address space and the transition of
   Internet infrastructure to IPv6, it is necessary to address the way
   in which email services can be transitioned from an IPv4 transport to
   that of IPv6.  There are significant issues to be addressed around
   the matter of abuse in an IPv6 based environment which have been
   addressed and largely resolved when operating using IPv4 as a
   transport mechanism.

   The majority of email service providers currently utilize IPv4
   blocklists to reject mail.  This is frequently done upon the initial
   email connection or sometime during the SMTP transaction (e.g., after
   the HELO, MAIL FROM or RCPT TO).  This is done to (a) save on more
   expensive downstream content filtering, (b) reduce the amount of spam
   that must be stored for the user in a spam folder, and (c) improve
   the quality of spam filtering.

   IPv4 blocklists are manageable because the size of IPv4 address space
   is approximately 4 billion IPs.  Even if in the worst case every
   single IP were listed, this is very large but still manageable for
   email filters with sufficient hardware.  The size of the total IPv6
   address space is 340 trillion trillion trillion IP addresses.  This
   is far too large for filters to handle or backend hardware to process
   or maintain.

   Even if blocklist maintainers listed only the IPs that were spamming,
   a spammer could send spam from an IP address, let the IP it used get
   listed on a blocklist, but discard that IP and move onto the next IP
   address.  By rotating through IPs quickly, a blocklist would always

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   be one step behind spammers and lose its effectiveness.  This would
   also result in more spam in users' inboxes, and greatly increased
   processing load for mail filters.

3.  Transition Model - Whitelists

   It is assumed that eventually the Internet will come up with a
   permanent solution to email over IPv6.  In the meantime, a transition
   model will be required.

   Rather than using IP blocklists to reject mail from known bad IPs,
   email receivers who wish to receive email over IPv6 should use
   whitelists to only accept mail from known good IPs and reject all
   email from IPv6 IPs that are not on the list.  This IPv6 whitelist is
   a "Do not reject all mail from this IP" list, email from these IPs
   may still go through traditional content filtering.  IPs on this
   whitelist are there because they send email over IPv6 intentionally,
   not because they are part of a botnet and are sending email without
   the computer owner's consent.

   It is not unusual for email receivers in modern spam filters to use
   whitelists, or "do not block" lists but still content filter the
   mail.  For example, many large email receivers do not block the IP
   ranges of large webmail providers but still apply content filtering.
   Other email receivers implement whitelists wherein a small set of IP
   addresses undergo no spam filtering.

   A flowchart of the process is below:

                    | Inbound mail |
                    |   arrives    |
          +-- No -- / Is sending \ -- Yes --+
          |         \  IP IPv6?  /          |
          |          \----------/           |
          |                                 |
   +------------+                  /-------------------\
   |  Continue  |                 /   Is sending IP     \
   |   normal   |       +-- No -- \ on IPv6 allow list? / -- Yes --+
   | processing |       |          \-------------------/           |
   +------------+       |                                          |
                        |                                          |
                 +-------------+                          +------------+
                 | Reject mail |                          |  Continue  |
                 +-------------+                          |   normal   |
                                                          | processing |

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   Using an IPv6 whitelist has the following advantages:

   (a) It allows email communication between those Internet users who
       need to do it over IPv6 instead of IPv4.

   (b) It does not permit widespread abuse of email over IPv6 since
       senders must make an effort to get onto the whitelist.

   (c) The lists will not take up much memory or bandwidth since the
       total amount of legitimate senders over IPv6 is projected to be
       substantially fewer than the total amount of Internet users or
       devices.  There simply are not that many senders who require
       sending email over IPv6, less than 20 million which is smaller
       than many IPv4 blocklists.

   It is not unusual to put restrictions on IPs that are newly sending
   email.  Today (2012) on IPv4, Internet users cannot simply start
   sending email out a new IP without encountering problems; most spam
   filters will view mail from a new IP as abusive and either block it
   or throttle mail from it.  Therefore, representatives between those
   users contact each other, informing them to expect to see mail from
   their dormant IPs in the near future, or else they ask for a pre-
   emptive whitelisting.  Thus, using an IPv6 whitelist already has
   precedent.  Just as new senders in IPv4 request pre-emptive
   whitelisting as a courtesy, in IPv6 they will have to request pre-
   emptive whitelisting as a requirement.

4.  Population of the IPv6 whitelists

   It is outside the scope of this Internet Draft to specify how an
   email receiver should build their own IPv6 whitelists.
   Administrators may contact each other by email over IPv4, by
   telephone, by regular mail, by word-of-mouth, or any other form of
   communication.  However, once one party or both parties have agreed
   to whitelist each other, they must add the others' IP or IPs to their
   whitelist.  They may continue to filter the message in the content
   filter and either store it in the user's spam quarantine, or reject
   the message based upon spam content, but they must not block messages
   from those IPs because of an IP filtering ban because the sending IP
   is IPv6.

   If any IPs from either party do send over IPv6 but are not included

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   in the whitelist because they were not agreed to previously, email
   from these IPs should be rejected.

   IPs in the whitelist can be either single IPs or in IP ranges, it is
   up to the receiver to decide which format to use.

5.  Security Considerations

   This document does not address any security issues inherent in IPv6
   Itself with the exception of IP blocklists.  It acknowledges that
   there are as yet unresolved abuse issues specific to deploying email
   infrastructures based on an IPv6 transport.  Abuse issues include
   general spam, phishing and spoofing of email addresses.

6.  Privacy Considerations

   This document describes at a high level activities that ISPs should
   be sensitive to, where the collection or communication of PII may be
   possible.  In addition, when performing this transition, ISPs should
   be careful to protect any PII collected whether deliberately or

   As noted, any sharing of data from the user to the ISP and/or
   authorized third parties should be done on an opt-in basis.
   Additionally the ISP and or authorized third parties should clearly
   state what data will be shared and with whom the data will be shared

   Lastly, there my be legal requirements in particular legal
   jurisdictions concerning how long any subscriber-related or other
   data is retained, of which an ISP operating in such a jurisdiction
   should be aware and with which an ISP should comply.

7.  IANA Considerations

   There are no IANA considerations in this document.

8.  Acknowledgements

   The authors wish to acknowledge the following individuals and groups

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   for performing a detailed review of this document and/or providing
   comments and feedback that helped to improve and evolve this

   None as yet

   Large section of this document are based ...

19.  Informative references

   [RFC1958]  Carpenter, B., "Architectural Principles of the Internet",
              RFC 1958, June 1996.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213, October 2005.

   [RFC5211]  Curran, J., "An Internet Transition Plan", RFC 5211,
              July 2008.

Appendix A.  Document Change Log

   [RFC Editor: This section is to be removed before publication]

   -01 version:

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   o  -01 version published

Appendix B.  Open Issues

   [RFC Editor: This section is to be removed before publication]

   No open issues to date

Authors' Addresses

   Terry Zink
   1 Microsoft Way
   Redmond, WA  98052

   Email: tzink@microsoft.com
   URI:   http://www.microsoft.com

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