[Exim] checking received header path before delivery

While trying to secure an intranet mailing list to only permit mail
sent from inside an organisation, I'm trying to achieve a routing
objective based on the received headers of a message. Obviously,
only the last few from trusted hosts can be used. An external-to
exim perl application provides the filtering.

Ideally, something like queryprogram which passed a full set of
headers via stdin would be ideal, but instead I think the only
solution is to use a pipe transport which reinjects the message
as appropriate with modified headers/delivery type, or rejects
it via the return_output interface.

Is there a better interface to achieve this end? I'd rather not
deal with the size restrictions and other limitations inherent
in using the string expansion copies of the headers.

B>
--
Packrat (BSc/BE;COSO;Wombat Implementor)
Nihil illegitemi carbovndvm