Individual submission M. Kucherawy
Internet-Draft Cloudmark
Intended status: Standards Track D. Crocker
Expires: October 28, 2012 Brandenburg InternetWorking
April 26, 2012
Email Greylisting: An Applicability Statement for SMTP
draft-ietf-appsawg-greylisting-09
Abstract
This document describes the art of email greylisting, the practice of
providing temporarily degraded service to unknown email clients as an
anti-abuse mechanism.
Greylisting is an established mechanism deemed essential to the
repertoire of current anti-abuse email filtering systems.
Status of this Memo
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This Internet-Draft will expire on October 28, 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
2. Types of Greylisting . . . . . . . . . . . . . . . . . . . . . 4
2.1. Connection-Level Greylisting . . . . . . . . . . . . . . . 4
2.2. SMTP HELO/EHLO Greylisting . . . . . . . . . . . . . . . . 5
2.3. SMTP MAIL Greylisting . . . . . . . . . . . . . . . . . . 5
2.4. SMTP RCPT Greylisting . . . . . . . . . . . . . . . . . . 5
2.5. SMTP DATA Greylisting . . . . . . . . . . . . . . . . . . 6
2.6. Additional Heuristics . . . . . . . . . . . . . . . . . . 7
2.7. Exceptions . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Benefits and Costs . . . . . . . . . . . . . . . . . . . . . . 8
4. Unintended Consequences . . . . . . . . . . . . . . . . . . . 9
4.1. Unintended Mail Delivery Failures . . . . . . . . . . . . 9
4.2. Unintended SMTP Client Failures . . . . . . . . . . . . . 10
4.3. Address Space Saturation . . . . . . . . . . . . . . . . . 11
5. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 12
6. Measuring Effectiveness . . . . . . . . . . . . . . . . . . . 13
7. IPv6 Applicability . . . . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9.1. Tradeoffs . . . . . . . . . . . . . . . . . . . . . . . . 14
9.2. Database . . . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . . 15
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
Preferred techniques for handling email abuse explicitly identify
good actors and bad actors, giving each significantly different
qualities service. In some cases an actor does not have a known
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