On Tue, 8 Oct 2019 08:52:11 -0400 Greg Wooledge <wool...@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 <deb...@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
