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 draft-tzink-ipv6mail-whitelist-00 Abstract 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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on March 15, 2012. Copyright Notice Copyright (c) 2012 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 Zink Expires November 15, 2012 [Page 1] Internet-Draft Transition of email services to IPv6 September 2012 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 contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Zink Expires November 15, 2012 [Page 2] Internet-Draft Transition of email services to IPv6 May 2012 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 Zink Expires November 15, 2012 [Page 3] Internet-Draft Transition of email services to IPv6 May 2012 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. Zink Expires November 15, 2012 [Page 4] Internet-Draft Transition of email services to IPv6 May 2012 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 community. 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 Zink Expires November 15, 2012 [Page 5] Internet-Draft Transition of email services to IPv6 May 2012 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 | +------------+ Zink Expires November 15, 2012 [Page 6] Internet-Draft Transition of email services to IPv6 May 2012 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 Zink Expires November 15, 2012 [Page 7] Internet-Draft Transition of email services to IPv6 May 2012 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 inadvertently. 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 with. 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 Zink Expires November 15, 2012 [Page 8] Internet-Draft Transition of email services to IPv6 May 2012 for performing a detailed review of this document and/or providing comments and feedback that helped to improve and evolve this document: 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: Zink Expires November 15, 2012 [Page 9] Internet-Draft Transition of email services to IPv6 May 2012 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 Microsoft 1 Microsoft Way Redmond, WA 98052 US Email: tzink@microsoft.com URI: http://www.microsoft.com Zink Expires November 15, 2012 [Page 10]