[Exim] Blocking Attachments

Hi,

A company I contract to wishes to allow some users to send attachments, and
block the rest, although they still want everyone to be able to send and
recieve email.

We run exim3.1x. Does anyone know how I can go about implementing this?

Please reply to the address below rather than the list.

Thanks in advance...

Kind Regards
--
Chris Massam <chris.massam@???>