[Mimedefang] MX -> 127.0.0.1

[Matthew.van.Eerde at hbinc.com]

Les Mikesell wrote:
> On Tue, 2005-09-13 at 13:33, Jim McCullars wrote:
>>> 
>>> It's unlikely you are talking to the original sender.  Assume a
>>> forwarding relay has accepted a copy (as I am doing now), then
>>> trying to deliver.

Depending on your topology, that "assumption" may be a certainty - or it may be a jump to conclusions.

>>> If you give a 5xx smtp response you force the
>>> sending relay to construct a bounce.  But you know it's impossible
>>> to deliver it.

Only given the assumption above.  If the sending agent is NOT a relay, but is instead the sending domain's MSA, then the bounce message will be constructed and delivered directly to the sender without any need for further SMTP at all.  Exchange works like this, for example.

>>    If the forwarding relay cannot construct a bounce, it really has
>> no business accepting the mail in the first place.
> 
> None of us here can determine that yet or we wouldn't be talking
> about how to do it... Isn't it a bit much to expect everyone else to
> already be checking?

http://www.digital-sledgehammer.com/superchicken/sounds/dangerous.wav

>> Besides, just because you
>> cannot deliver a bounce, that doesn't mean the forwarding relay
>> cannot. An internal DNS, or mailertable are two ways that it could.
> 
> Anyone who has gone to the trouble of poisoning public DNS with an
> MX that ends up at 127.0.0.1 really doesn't want that bounce back
> so I think we can assume they won't make an extra effort to make it
> work from certain machines.  Or, they just want to cause trouble
> for others and it becomes your choice to help them or not.

Maybe they put it in by mistake.  Bouncing at least gives them a hint.

-- 
Matthew.van.Eerde (at) hbinc.com               805.964.4554 x902
Hispanic Business Inc./HireDiversity.com       Software Engineer