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

2019-12-21 14:40:44
On Dec 21, 2019, at 10:00 AM, Hector Santos <hsantos(_at_)isdg(_dot_)net> 
wrote:

I believe the SMTP "ideal" MTA auto setup is:

(1)  Set Client.IP from Sender Session Connection IP

(2)  Set EHLO.field from manual configuration/definition

This is what Postfix does by default:

        myhostname = <system hostname, with .$mydomain if not fqdn>
        smtp_helo_name = $myhostname

Either or both can be set explicitly.

(3.1)  if EHLO.FIELD is empty then EHLO.FIELD = using socket gethost() for 
client.ip

This is not robust in the face of temporary lookup failures, so we don't do
that.

(3.2)  if EHLO.FIELD is empty then EHLO.FIELD = get first PTR for client.ip

Ditto.

(4)  if EHLO.FIELD is empty, then EHLO.FIELD = "[" + Client.IP= "]"

This is frowned upon by receiving systems, we don't do that.

Not every MTA does #2.  Not every MTA has a dns resolver,

Those that don't, do send email to across the public Internet, so
are out of scope for this thread.

so it may not do 3.2, but it may do 3.1 and the behavior depends on the OS 
socket stack.  But going direct to DNS (3.1) is generally the right way.

Well, my take is that #2 is the preferred (robust, dare I say "deterministic")
approach.

-- 
        Viktor.

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