Re: domain names, was: hostname
On Thu 22 Feb 2018 at 11:58:18 -0600, David Wright wrote:
> On Mon 19 Feb 2018 at 18:39:02 (+0000), Brian wrote:
> > On Mon 19 Feb 2018 at 10:23:56 -0600, David Wright wrote:
> >
> > > 127.0.0.1 localhost
> > > 127.0.1.1 alum
> >
> > alum is the canonical_hostname. It is used by exim to HELO with. Many
> > mail servers will not accept mail directly from you because it is not a
> > FQDN.
>
> This is why I wrote "broken" at ². The OP wrote "on a home LAN",
> in which case it's unlikely that they relay mail to mail servers
> on port 25. More likely is that they use a smarthost with a mail
> submission system on port 587 or possibly 465 (though 25 is
> allowed for broken senders³).
Not using a smarthost does not invalidate the claim.
> As submission involves obligatory authentication, there's no reason
> to reject a submission just because the HELO has no dot in it. And
> even if a sender screws up the envelope-from, it's likely that the
> mail submission knows a valid email address associated with the
> authenticator's registration details.
With
127.0.1.1 gmail
in /etc/hosts the conversation would go like this:
brian@desktop:~$ telnet bendel.debian.org 25
Trying 82.195.75.100...
Connected to bendel.debian.org.
Escape character is '^]'.
220 bendel.debian.org ESMTP Postfix
helo gmail
250 bendel.debian.org
mail from:<someone@debian.org>
250 2.1.0 Ok
rcpt to:<debian-user@lists.debian.org>
504 5.5.2 <gmail>: Helo command rejected: need fully-qualified hostname
gmail.com is ok with bendel.
OTOH:
brian@desktop:~$ telnet cloud11.unlimitedwebhosting.co.uk 25
Trying 149.255.60.164...
Connected to cloud11.unlimitedwebhosting.co.uk.
Escape character is '^]'.
220 cloud11.unlimitedwebhosting.co.uk ESMTP Postfix
helo gmail
250 cloud11.unlimitedwebhosting.co.uk
mail from:<someone@debian.org>
250 2.1.0 Ok
rcpt to:<deblis@lionunicorn.co.uk>
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
cloud11.unlimitedwebhosting.co.uk appears not to be bothered by the
helo; bendel is.
> > > I've sometimes wondered what other people dream up as their
> > > domainnames; that is, people who don't have a legitimate reason
> > > to put something like example.com.
> >
> > Whatever is dreamt up as a domain name is put into /etc/hosts by the
> > installer as
> >
> > 127.0.1.1 alum.dreamtup alum
>
> And what is the benefit for the mail submission system in being woken
> up with HELO alum.dreamtup rather than HELO alum ?
> Extra brownie points for imagination perhaps.
Most large ISPs presumably do not see any benefit as they basically
ignore an RFC non-compliant helo. The large number of broken mailers
about might be a reason. I'm not prepared to risk having mail rejected
because the canonical_hostname is not a FQDN known in the DNS.
--
Brian.
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