* Philip Hazel:
> On a matter of technical detail: I don't think it should be a global
> option (in the Exim 3 style). It should, if implemented, be another
> sub-option of the "callout" option in the ACL.
>
> verify = sender/callout,postmaster,postmaster_sender=xxxx
This is a bit dangerous because it can easily result in loops. The
empty sender avoids this problem.