[exim] Exim filter woes

Hi Guys

I am trying to write a filter to do an undeen delivery to darren when
mail is sent to petro.

This is what I have at the mo but it isn't working :(

Any help would be appreciated.

Thanks
c

System_filter:
--------------

# Exim filter

if not first_delivery
then
finish
endif

if ${lc:$sender_address} is "petro@???"
then
    unseen deliver "<darren@???>"
Endif

Exim.conf:
----------

system_filter = /etc/mail/system_filter
system_filter_user = mail