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Re: [ietf-smtp] IETF Policy on dogfood consumption or avoidance - SMTP version

2019-12-26 07:19:24
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In message 
Keith Moore <moore(_at_)network-heretics(_dot_)com> writes

   Yes.  But "good practice" is in keeping with the purpose of EHLO, 
   which is _not_ intended to be used for spam filtering.   Any spam 
   filtering practice based on EHLO tags is inherently dubious.   Even 
   if it happens to "work" for some site or another at some particular 
   time, it's not defensible as good practice in general.

The highly effective spam filtering performed by the giants (who handle
billions of emails a day) is done by "machine learning" classifiers.

These classifiers collect a wide range of indicators of which EHLO (and
indeed HELO) will be one contributor of a numeric value indicating some
sort of view "correctness" or perhaps just a score to indicate the type
of string presented. These values will contribute to the classification
of email into spam/non-spam accept/reject etc.

It would not be expected that any particular feature would by itself
provide reliable classification -- hence the ubiquity of ML. Also
(depending on the type of ML used) it may be hard to say what exact
contribution towards the final decision is being made by any particular
feature (viz: we're not going to settle the present discussion by asking
AOL, Apple, Google, Microsoft and Yahoo whether HELO/EHLO matters
because they may well not know -- and the answer may vary week by week).

It should also be noted that the most competent senders of spam are
often the most squeaky-clean when it comes to conformance to the RFCs
(they send enough to quickly learn when their set-up is affecting their
delivery rates) and it is only the sloppier spammers and the rather more
slap-dash (or indeed the most set-up challenged) of legitimate senders
who fail to conform.

There are no silver bullets in this space -- and impacting legitimate
senders is seldom a way to improve customer satisfaction with your mail
reception service.

- -- 
richard                                                   Richard Clayton

Those who would give up essential Liberty, to purchase a little temporary 
Safety, deserve neither Liberty nor Safety. Benjamin Franklin 11 Nov 1755

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