Re: [exim4] Testing and making sense of smtp output
On Mon 13 Oct 2014 at 10:51:51 +0100, Joe wrote:
> On Mon, 13 Oct 2014 10:25:37 +0100
> Brian <ad44@cityscape.co.uk> wrote:
>
> > On Mon 13 Oct 2014 at 04:06:27 +0200, lee wrote:
> >
> > > Harry Putnam <reader@newsguy.com> writes:
> > >
> > > > lee <lee@yagibdah.de> writes:
> > > >
> > > > [...]
> > > >
> > > > Thanks for the tips.
> > > >
> > > >>> SMTP>> EHLO 2xd
> > > >
> > > >> That's an invalid helo string.
> > > >
> > > > Is a valid one made up of just the full fqdn?
> > >
> > > See https://tools.ietf.org/html/rfc2821#section-4.1.1.1
> > >
> > > It says to either use the fqdn or, if not possible, an IP
> > > literal. However, it's common practise to deny IP addresses in HELO
> > > greatings.
> >
> > An address literal is not the same as an IP address. An MTA should not
> > be rejecting mail on the basis that the HELO is an address literal.
> >
> > It's probably academic what the HELO is most of the time. Many ISPs
> > will accept any old rubbish for it.
>
> The routine exim4 HELO test is disabled by default, but simply checks
> that it is a hostname which can be resolved in public DNS. I enable it,
> and so do a lot of others. It is by default enabled in Exchange, which
> is in widespread use, and I've seen an Exchange server reject an email
> arriving from a BT server which had a '.local' TLD in its HELO.
Four ISPs in the UK have over 90% of the market. None of the four
appears to be the least bit bothered about HELO as "AutumnLeaves".
On the basis that it is invalid a few of the smaller ones are but then
proceed when given "AutumnLeaves.com".
Not that I'm suggesting setting up exim to offer an invalid HELO; it
will lead to trouble sooner or later. However, as a reason for mail
being rejected or not arriving it doesn't come top of the list.
Reply to: