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:
> > 
> > >       localhost
> > >       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       gmail

in /etc/hosts the conversation would go like this:

  brian@desktop:~$ telnet bendel.debian.org 25
  Connected to bendel.debian.org.
  Escape character is '^]'.
  220 bendel.debian.org ESMTP Postfix
  helo gmail
  250 bendel.debian.org
  mail from:<some...@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.


  brian@desktop:~$ telnet cloud11.unlimitedwebhosting.co.uk 25
  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:<some...@debian.org>
  250 2.1.0 Ok
  rcpt to:<deb...@lionunicorn.co.uk>
  250 2.1.5 Ok
  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
> > 
> >   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.


Reply via email to