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Re: Federated, decentralised communication on the internet (was: domain names, was: hostname)

On Thu, 22 Mar 2018 08:59:11 +0100
deloptes <deloptes@gmail.com> wrote:

> David Wright wrote:
> > Sure, so in my case, I'd be forced to find out what my router's
> > hostname is so that I can quote a hostname that will resolve to the
> > address that I woud be posting on. Currently this appears to be
> > ip70-179-161-106.fv.ks.cox.net  
> these are not valid SMTP domain names. It might be valid FQDN, but the
> server on the other end is most likely to reject it.

It doesn't need to be a mail domain, it's a hostname. What is important
is that it:

a) exists, and
b) that a DNS lookup returns the same IP address, 

i.e. there is an A record which points to an IP address and a PTR
record for the IP address that points back to the same A record. Note
that these are often maintained by different companies: the owner of
the IP address, the ISP, maintains the PTR record (and may allow the
user to do so) and the domain name host maintains the A record. It
isn't normally necessary for this hostname to have any connection with
any email address or HELO.

Unfortunately, many domestic ISPs now maintain this relationship even
on their dynamic addresses, so it is becoming less useful in
identifying spammers.

> > but it changes at random times governed by I know not what.
> > But wait: to post from any of my machines, they all have to have
> > ip70-179-161-106.fv.ks.cox.net in /etc/hosts so that exim uses it
> > as the HELO string. This to an ISP that knows which wire I'm
> > connected to at their end.  
> Best is to use dynamic DNS or DDNS service, but I am not sure if the
> free versions support MX records (most probably not)

About ten years ago, when I was active on the MS Small Business Server
newsgroup/forum, it was often claimed that it was practical to run a
mail server on DDNS. 


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