On 12/21/19 3:40 PM, Viktor Dukhovni wrote:
(4) if EHLO.FIELD is empty, then EHLO.FIELD = "[" + Client.IP= "]"
This is frowned upon by receiving systems, we don't do that.
So if you don't have an explicitly configured hostname, do you simply
refuse to send messages? Or send EHLO example.com? or what?
DNS is nowhere nearly universal, and cannot be. Using an IP address
literal in EHLO makes perfect sense, at least for systems forwarding to
a private submission server. And there are so many of those systems
out there that requiring explicit configuration for all of them might
not be the best choice.
(As for the notion that "real MTAs have DNS names", I think that even
that's a stretch. People are constantly making dubious assertions
about what "real systems" do or should do. But the Internet is
necessarily a tremendously diverse place and it's easy to overlook some
important corner case when making such sweeping assertions.)
Keith
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