[nzlug] (OT) Sorbs etc, was Exim: Limiting outgoing connections on Debian

[Cliff Pratt]

Daniel Pittman wrote:
> Cliff Pratt <enkidu at cliffp.com> writes:
>> Donald Gordon wrote:
>>> On Fri, 06 Oct 2006 15:12:37 +1300, Tony Wills <ajwills at paradise.net.nz> wrote:
>>>
>>>> I still get tons of SPAM via my ISP (although the amount that
>>>> they're syphoning into the Spam folder at their end seems to have
>>>> diminished).  I get none through my own server which uses
>>>> greylisting - a very effective idea for small email servers - I get
>>>> an awful lot of "unexpected disconnectsion"s from spammers that are
>>>> asked to wait :-)
>>> Greylisting is not terribly wonderful.  It cuts down on some spam,
>>> but breaks an expectation that many users have: that their email is
>>> sent instantaneously.  And I have a client whose odd Mac-based
>>> mailserver package doesn't know what retrying is :-(
>> Greylisting is an evil perversion of the SMTP protocol and if I find
>> any servers using it I blacklist them. Nasty obnoxious bandwidth and
>> spool space wasters!
> 
> I don't think that word means what you think it means...
> 
> The SMTP protocol defined soft error cases specifically because there
> *are* cases where a later attempt to deliver the same message will
> succeed.
> 
> The traditional examples were a host that had mail down for maintenance,
> a mailbox over quota or a site that was under too much load.[1]
> 
> 
> So, whatever else greylisting may be, it is *not* a perversion of the
> SMTP protocol.  It is, in fact, a use of the SMTP protocol as designed.
> 
> That fact doesn't contribute anything to the debate on the use of
> greylisting, but neither do false claims about "perversion" of
> protocols.
> 
"Perversion" has, these days, unpleasant connotations that I did not 
intend. I was thinking of the word in the sense of the "WordNet" 
definition on Dictionary.com: "The action of perverting something 
(turning it to a wrong use)".

I'm not going to prolong the discussion on this topic, so my final word 
is that I dispute that greylisting is a "use of the protocol as 
designed". The temporary error facility is intended to provide the 
ability to recover from a situation, as you say, where the receiving 
SMTP server is unable to accept the message. In other words, it was for 
the benefit of the sender. It was never intended to introduce an 
intentional delay and was never intended to be used to the benefit of 
the receiving SMTP server!

Cheers.

Cliff