Re: et.al., (was: Dependencies et al, was: Default Debian install harassed me)

[Joe <joe@jretrading.com>]

On Tue, 8 Oct 2019 08:52:11 -0400
Greg Wooledge <wooledg@eeg.ccf.org> wrote:

> On Tue, Oct 08, 2019 at 09:13:31AM +0100, Joe wrote:
> > On Tue, 8 Oct 2019 00:25:44 -0500
> > David Wright <deblis@lionunicorn.co.uk> wrote:  
> > > Why would you use a "subscribed.address" (presumably an email
> > > address) for your HELO (presumably actually a EHLO). I was under
> > > the impression that it should be a domain, ie a FQDN.  
> > 
> > It should actually be a hostname, it's the official public name of
> > the mail server, though not of course its local network name. It
> > must be resolvable in public DNS. In practice, not much of this is
> > enforced, and you can get away with a domain name and, apparently,
> > an email address.  
> 
> "Enforcement" is entirely up to the receiver's discretion. 

Yes, that's what I meant, there's nobody else to enforce anything. But
I've never had an email rejected for a mismatched HELO.

> Some
> receivers use it as an anti-spam measure -- if your HELO string
> doesn't resolve, they won't accept your connection.

Yes, I do that, and I think it's the default for Exchange servers. A
look through the Exim configuration file gives a lot of anti-spam hints
in terms of the built-in options.

>  I've even heard
> of receivers who attempt to make an STMP connection back to the MX of
> your HELO domain, to make sure you have a running incoming SMTP
> service.
> 
I haven't seen that one, that I'm aware of. But that presumably is
circumvented simply by using a HELO for a domain that is known to run a
mail server. In the days when I used Telnet to talk to mail servers, I
used a well-known six-character domain name for my HELO for brevity,
with which I had no connection whatever. No server ever refused it.

> Other receivers may simply log it, or ignore it altogether.
> 

Indeed, but it's of value. A lot of people seem to think that using
their IP address, or my own IP address or domain name as their HELO is
clever.

-- 
Joe