>>> Their exchange server is (by default) setup to accept all messages to
>>> anyuser@???
>>> and then bounce the names that do not exist.
>>
>> This is default behaviour (for Exchange 2003 at least, and probably
>> earlier versions).
>>
>
> The default behaviour for all versions is to accept everything for the
> local domains. And, AFAIK, there is no easy "MS only" way to solve this
> before 2003 version.
An LDAP lookup against Active Directory is the only sensible way pre
Exch2003. Peter Savitch posted some code to the Exim wiki for this:
http://wiki.exim.org/MsExchangeAddressVerification
The filter option is fine for Exch2003, but Exch2007 users will now need a
64bit "Edge Transport Server" to do this, and it has to be run on a
separate/dedicated box with 2GB ram according to the docs. More info here:
http://www.exim-new-users.co.uk/Integrating_Exim_With_Groupware_Servers_v1.0.pdf
Thanks
Jason_Meers