[ietf-dkim] Are subdomains like parent domains?
chl at clerew.man.ac.uk
Tue Apr 29 02:37:02 PDT 2008
On Tue, 29 Apr 2008 01:25:26 +0100, John Levine <johnl at iecc.com> wrote:
>>> But I have to say, without any sort of domain blanket/coverage
>>> option, it seems like something is really missing here.
> I'm seeing an implicit assumption that if someone has an opinion about
> mail from foo.com, they will have a similar opinion of mail from
> subdomains a.foo.com or a.b.foo.com, or a.b.c.foo.com. I've been
> thinking about the mail I actually see, and I am having great
> difficulty finding even a small set of real life scenarios where that
> is true.
> For corporate or ISP domains, they either use one domain for all the
> mail, e.g. aol.com, or a handful of regional or divisional subdomains,
> e.g. twcny.rr.com or watson.ibm.com. The other 99% of the names under
> the main domain are random hosts whose names are unlikely to appear as
> mail addresses* in real mail.
Not necessarily so. The machine random.example.com, which sits on some
secretary's desk somewhere, is likely to have an MX record pointing to
mail.example.com. So all outgoing mail will go through mail.example.com
(it will be the machine appearing in the EHLO). And the postmaster at
example.com will ensure that all such necessary MX records are set up.
But the problem is what goes in the From header of mails coming from
random.example.com? Those will be set by whatever MUA is running on that
secretary's machine which, if that machine was configured by the Secratary
herself, will most likely be left by default at random.example.com.
Now a smart postmaster who is an expert in hacking sendmail.cf may well
arrange to have that From header fixed before it goes out, but don't bank
on it. And what happens if the secretary wamts to set the From header to
something completely different, e.g. From: boss at somewhere.example.com with
Sender: secretary.example.com? Don't tell me you have never seen that
particular scenario before :-).
Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131
Email: chl at clerew.man.ac.uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K.
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