[Exim] Parent addresses

Is there any way I can get at the list of all parent addresses during
processing of a director?

$original_domain and $original_local_part will give me the original
address, and $parent_domain and $parent_local_part will give me the
immediately preceding parent; is there any way I can get at all the
intermediate ones?

Thanks,
Chris.


(Just in case anyone wants more info: as per Philip's suggestion recently,
my first director is:

  # First check whether this is an error/warning, and if so deliver it to
  # postmaster on the local machine.
  checkerr:
    driver = smartuser
    condition = ${if eq {$sender_address}{} {yes}{no}}
    new_address = postmaster

However, this breaks because postmaster is an alias, and the newly-
generated address after aliasing gets passed to the checkerr director
again, which means it just gets turned straight back into postmaster.
Ideally I'd like a condition on checkerr which says "if any of the parent
addresses are equal to postmaster, don't run this director".)