--On 30 March 2006 16:16:09 +0100 Adam Funk <adam00f@???> wrote:
> On 2006-03-30, Peter Bowyer <peter@???> wrote:
>> On 30/03/06, Adam Funk <adam00f@???> wrote:
>>> On 2006-03-30, Nigel Wade <nmw@???> wrote:
>>>
>>> > That only works for mis-configured MTAs. A properly configured MTA
>>> > would reject a message destined for a non-existent recipient. It
>>> > would not accept it and then generate a bounce message.
>>>
>>> But when MTA(n) rejects a message that MTA(n-1) is trying to relay,
>>> MTA(n-1) has to bounce it, right?
>>
>> MTA(n-1) shouldn't accept messages to invalid recipients in the first
>> place. If it has no direct knowledge of valid recipients, it should do
>> callouts.
>
> I understood those weren't reliable because (there may be other
> reasons?) in many cases MTA(n) is configured not to give out that
> information because spammers could use it.
Well, heck... If the MTA accepts good addresses, but rejects bad ones, then
it's not too hard to figure out which the good ones are! If they accept all
local addresses, then they have to bounce the bad ones, and then they leak
the information.
No, you can't run a proper MTA and NOT leak information about what the good
addresses are. That would be equivalent to the Post Office dumping all
undeliverable mail in the sea!
--
Ian Eiloart
IT Services, University of Sussex
