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 184.108.40.206... 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:<email@example.com> 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 220.127.116.11... 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 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.