Re: domain names, was: hostname

[David Wright <deblis@lionunicorn.co.uk>]

On Fri 23 Mar 2018 at 11:59:06 (-0400), Miles Fidelman wrote:
> On 3/22/18 10:03 PM, David Wright wrote:
> 
> >On Thu 22 Mar 2018 at 20:26:26 (+0000), Brian wrote:
> >>On Thu 22 Mar 2018 at 12:44:53 -0500, David Wright wrote:
> >>
> >>[...]
> >>
> >>>Here are my points, as it's a month since I made them. I didn't
> >>>quite answer the question as posed.
> >>>
> >>>--✄------
> >>>
> >>>>that as well as being asked to supply a hostname I've also been asked
> >>>>to supply a domain value.
> >>>>
> >>>>What, on a home LAN, is that used for?
> >>>Nothing, with the possible exceptions of:
> >>>
> >>>. avoiding this message at boot up:
> >>>   Mon Feb 19 04:58:38 2018: [....] Starting MTA:hostname --fqdn did not return a fully qualified name,
> >>>   Mon Feb 19 04:58:38 2018: dc_minimaldns will not work. Please fix your /etc/hosts setup.
> >>>
> >>>. satisfying a broken smarthost¹,
> >>>
> >>>. causing some discussion here.
> >>>
> One possible additional consideration:
> 
> Home machines are often behind a NAT router - the real IP address of
> the machine is that of the network side of the router.

Yes, see the first paragraph of my previous post where I used
the word "forced" in a way that caused some dismay,
https://lists.debian.org/debian-user/2018/03/msg00799.html
(and where I also forgot to revert the Subject line).

> Some spam filters do reverse lookups on IP addresses in mail
> headers.  And, depending on what headers they validate, if your
> outgoing messages contain an IP address that doesn't resolve to the
> domain of your router - funny things might happen.
> 
> Given how much spam originates from botnet-infected home machines,
> and/or use forged sender information, I would not be surprised if
> some spam filters aren't checking the originating header for
> consistency.
> 
> At some point, the network name that one's PC inserts into outgoing
> mail might become important.

I venture to suggest that many (most?) .home users will be using their
ISP's smarthost, which would mean that the ISP (a) usually insist on
authentication and (b) and likely to have issued the network name
(like ip70-179-161-106.fv.ks.cox.net) themselves.

Cheers,
David.