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Re: 4yz Temporary Rejections is part of the SMTP Protocol

2011-10-27 17:26:35



--On Thursday, October 27, 2011 17:01 -0400 Hector Santos
<hsantos(_at_)santronics(_dot_)com> wrote:

...
One may suggest SMTP did document the basic idea of
greylisting by using the term "temporary" for a 4yz reply
code.  It just keep it open ended and did not get into ideas
of what is "temporary" and/or how it relates to "time."

Without trying to split this set of hairs further, I suggest
that a key property of the original SMTP use of 4yz codes was
that they were reporting an inability to continue that was
outside the control of the SMTP server itself.  "Connection
going down", "temporary lack of storage to add to user mailbox",
"System shutting down", etc., are all examples of that
situation.  "I'm going to deliberately put stumbling blocks in
your path so that maybe, if you are a bad guy, you will just go
away" was certainly not part of that model.  

As I tried to say in an earlier note, whether use of 4yz codes
in an attempt to block spam, or even as a traffic control
measure, is a clever extension of SMTP to use an existing
feature in a new way or a serious conception abuse of the base
protocol is mostly in the mind of the beholder.  But I don't
think it moves things forward to pretend that this sort of usage
was there all along.  

I'm not suggesting it, but, to the extent to which SMTP
extension are involved here (rather than a description of how to
use the base protocol in a particular way and improve
interoperability if it is used that way), one could even thinks
about a new series of reply codes for traffic management of
various types (6yx?  9yz?) rather than trying to do tricky
things with 4yz.  

   john

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