On 12/25/19 8:31 PM, John C Klensin wrote:
So, if it's a host name, it has to resolve. So,
'shortname.localdomain' wouldn't be valid.
The interesting thing to me is that if you don't have a valid
DNS name, an IP address literal seems like the right thing to
use. Even if behind a NAT at least it's some identifier that
is associated with the sending host that can go in a Received
header, still potentially useful for tracing if the server has
logs showing the source IP address. An EHLO tag based on a
boilerplate hostname and boilerplate suffix is essentially
useless for that purpose.
And, while the wording is different, that is essentially what
5321 (and 2821 before it) say. So I think you are suggesting
that the core requirement is fine and that, if anything is
needed, it is better language about when it may, or may not, be
a good practice.
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.
Keith
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