sink.arpa question

Pete Barnwell pete.barnwell at whole.net.uk
Sun Dec 20 16:14:32 CST 2009


Joe Greco wrote:
>> 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
>   

I'd think this more than common - the  A  record for the domain quite
often is set to point to the same IP as the www. A record where that 
server isn't running an smtp service.
We've certainly got clients who do this, and haven't ever reported it
causing problems = one example :-

banquo>host -t A www.thehut.com
www.thehut.com has address 89.234.46.152
banquo>host -t A thehut.com
thehut.com has address 89.234.46.152
banquo>host -t MX thehut.com
thehut.com mail is handled by 3 mail.thehutgroup.com.
banquo>host -t A mail.thehutgroup.com.
mail.thehutgroup.com has address 217.158.230.4

Regards

Pete






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