[exim] Re: bounce messages and their potential misuse

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.