[Exim] acl_check_rcpt ldap lookups

Hi Guys,

I'm wondering if it is possible to do ldap query for valid recipient in the
acl_check_rcpt portion of exim.
This would allow one to theoretically disallow mail to recipients who do not
have the correct group permissions.
If anyone has done this with an exchange server i'd also be quite interested
in seeing an example of the configs.

Regards
John