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Re: [ietf-smtp] Private Domain Names and the EHLO/HELO Command

2013-03-27 05:43:52
Sabahattin Gucukoglu <listsebby(_at_)me(_dot_)com> wrote:

Once again I am faced with the question of what to do (as a "Dumb" SMTP
client) when my outgoing interface has a private IP address and the name is
locally administered.

I saw your question on twitter, but 140 characters wasn't enough for an

There are about three cases to consider:

(1) This is excluded since you are asking about a dumb client, but for
mail across the public internet to an MX, the sender should be configured
to put a proper host name in its EHLO command.

(2) Client talking to an internal relay / smarthost.

(3) Message submission.

In the latter cases, and especially (3), pretty much anything is OK, since
the server has a relatively close relationship with the client. So the
client should just try to send something syntactically valid and not worry
too much about NAT making the client's view of the network appear nonsense
to the server.

For example, while a EHLO domain ending in .lan or .home is an almost
certain indication that the client is a spam bot in case (1), it's
OK and quite normal for (3).

If you are a client author, you need to be careful about host names
since they can contain surprising kinds of garbage.

f.anthony.n.finch  <dot(_at_)dotat(_dot_)at>
Forties, Cromarty: East, veering southeast, 4 or 5, occasionally 6 at first.
Rough, becoming slight or moderate. Showers, rain at first. Moderate or good,
occasionally poor at first.
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