[Mimedefang] MX -> 127.0.0.1

[Kevin A. McGrail]

How is this a hostile to the relay?  We aren't even accepting the mail.  We
are rejecting it before the conversation between the SMTP servers is
finished.  This email won't even hit your local queue.

> If the only or best MX target is 127.0.0.1, this is fairly hostile
> toward your neighbor relay.   But, as I mentioned before, the spam
> appliance I am forwarding through is doing a 451 temp_fail which
> just prolongs the problem and backs up my queue.  There's no chance
> that a notification is going to make it anywhere in this case
> so why not drop it?   On the other hand if there are multiple
> targets and some appear good, it might make sense to reject/bounce.
>
> A logical extension of this would be some way to parse your logs
> for repeated failures for bounce delivery attempts and add those
> to the bad address list.