Re: [exim] a large number of domains fronted by Exim are ref…

> The main
> argument here is that a valid reason to reject all <> is for
> mailboxes/domains that don't send mail -- so when your callout fails
> and you reject the message its all good.

Yes, this may be true for the envelope sender callouts (as far as I can
see).
But at the last time we see configurations which have special
return-path-addresses (SPF config and so on). These systems may don't
accept the null-reverse-path for their header senders (i.e. the normal
user mailboxes), cause they never use their normal mail addresses in the
return-path. Thats a very sophisticated mail setup and it breaks our
poor header sender callouts. Just these callouts caught so much spam in
the past.
;-(

- oliver