On Dec 21, 2019, at 3:47 PM, Keith Moore <moore(_at_)network-heretics(_dot_)com>
wrote:
So if you don't have an explicitly configured hostname, do you simply refuse to
send messages? Or send EHLO example.com? or what?
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".
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 <https://tools.ietf.org/html/rfc5321#section-4.1.3> and
discussed further in the EHLO discussion of
Section 4.1.4 <https://tools.ietf.org/html/rfc5321#section-4.1.4>.
So, if it's a host name, it has to resolve. So, 'shortname.localdomain'
wouldn't be valid.
--
Paul Smith Computer Services
Tel: 01484 855800
Vat No: GB 685 6987 53
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