On 2012-06-04 06:06, David Diggles wrote:
I was just thinking surely resending from a different IP breaks the RFC for
SMTP?
Then I did some googling, and found this.
http://bsdly.blogspot.com.au/2008/10/ietf-failed-to-account-for-greylisting.html
Not only is greylisting fine from a protocol point of view (as others
have pointed out), the IETF is also well aware of it. This is about to
become an RFC:
http://tools.ietf.org/html/draft-ietf-appsawg-greylisting
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.
Simon
