Joe Greco jgreco at
Sun Dec 20 11:05:15 CST 2009

> On Fri, 18 Dec 2009, Jason Bertoch wrote:
> > Do metrics exist on how many current installs still rely on the implicit
> > MX?
> It's very common for email from web servers to be poorly configured such
> that it uses the webserver's hostname as the return path's mail domain.

It is very difficult to measure how many current installs rely on the
implicit MX, as someone else noted.

On a somewhat different angle of attack:

Even five years ago, it was considered mildly problematic to deploy a
hostname where the A pointed someplace incapable of receiving mail,
since some "products" (you know who you are) were so poorly written
and still in use that they would connect to the A (or "implicit MX" 
if you prefer) even in the presence of MX records.

Now that another five years have passed, it would be interesting to
see how many antiques are still sending e-mail AND are worth talking
to.  I'm guessing not many.

That suggests that it might well be fine to point A at something that
is not capable of receiving SMTP, as long as you have MX records.  An
arrangement that should always have been practical, of course.

Is anyone actually doing this?

... JG
Joe Greco - Network Services - Milwaukee, WI -
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.

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