[exim] Detecting attachments using a transport_filter.

I've been asked by management (always a worrying way to start an email)
to setup a method of detecting attachments entering and leaving the
company via email. I've written a perl script to accept a message on
STDIN, break it down into its parts if it's MIME, detect if any of its
parts are non text/*, send an email to a nominated address and return
the message unedited on its STDOUT.

The problem I'm having is getting Exim to fire this script for each
message it sees. I've looked at a transport_filter, but I'm getting
errors in my mainlog when Exim tries to run this:
[snip]
2005-02-10 17:21:42 1CzHxD-0000Me-6J == test@??? R=amavis
T=amavis defer (-24): transport filter process failed (2)
[snip]

I've checked the permissions, and run the script as the Exim user. It
runs fine.

Is a transport_filter the best way to do this, or am I missing something
really obvious? If the latter, any pointers in the right direction would
be appreciated.

Thanks,

Carl
--
Carl C. Inglis
IT Systems Administrator
Total Recruitment/Skillwise Ltd.
Help Desk: 01724 273350