Re: Choice of "mailname" for mail server: suggestions welcome
On Fri, 21 Feb 2020 06:46:59 -0600
Tom Browder <tom.browder@gmail.com> wrote:
> On Fri, Feb 21, 2020 at 06:29 Joe <joe@jretrading.com> wrote:
>
> > On Fri, 21 Feb 2020 06:00:14 -0600
> > Tom Browder <tom.browder@gmail.com> wrote:
>
> ...
>
> > > As I understand it, a mail server has to use smtp to physically
> > > transfer mail between physical hosts and that requires one name
> > > that will resolve to an IP. Even if the server is hosting multiple
> > > domains, the mail for each still has to use the one "mailname" for
> > > transport.
> >
> > Not really, you can have an A record for each domain, with the MX
> > record for each domain pointing to its 'own' A record. The only
> > common feature must be the IP address that the A records point to.
> >
> > You may well have only one PTR record for the address, although
> > multiple PTRs on one address are valid, but not many ISPs make
> > provision for that.
> >
>
> Interesting--I would prefer that. So with all mail stuff on one
> server, I can have each domain's MX record point to its own mail
> server. And I do have control of the PTR record. I just need to
> ensure everything resolves to the correct host IP.
>
> So how does all that jibe with the single name required by OpenSMPTD?
>
Don't know, I'm not familiar with that. But mail server software
shouldn't need to know anything about the DNS records used to route SMTP
mail to it. If so configured, it will look up DNS records of senders,
but not generally its own.
Exim4 has a default mailname, but to the best of my knowledge, it is
used only in the HELO/EHLO banner, and can be overridden for multiple
domains. HELO/EHLO is used to identify the server in logs, and need not
have any relationship to any email domain handled by the server, and is
often (incorrectly) configured as a bare domain name. It is best
configured to the same FQDN that the domain's primary MX record holds.
It is certainly supposed to be a FQDN, and it does need to be
resolvable in public DNS. My mail server, like most, is configured to
reject email from a sender whose HELO is not resolvable, and
particularly those whose HELO appears to be my own domain or public IP
address (yes, some malware does that). DNS servers aren't really
supposed to resolve bare domain names, but most do, aliasing to the
'www' A record, because many people are too lazy to type 'www' in what
should be a web FQDN.
--
Joe
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