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

2019-12-21 16:50:59
On 12/21/19 5:28 PM, Paul Smith wrote:

There's always a hostname.  It defaults to the return value of gethostname().
And if that contains no dots, and "mydomain" is not set, then the domain
defaults to "localdomain".  So worst case you get "shortname.localdomain".

I expect that there are a lot of MTAs advertising EHLO raspberry.localdomain or debian.localdomain or some such.

But RFC 5321 says:
The domain name given in the EHLO command MUST be either a primary
       host name (a domain name that resolves to an address RR) or, if
       the host has no name, an address literal, as described in
       Section 4.1.3  <>  and 
discussed further in the EHLO discussion of
       Section 4.1.4  <>.

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.

Seen in that light, the IETF operators' filtering policy is looking less valid all the time.


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