[Exim] Filters

Hello all,

        I've been trying to get a filter file working to pass mails onto a
virus
checking program. My problem is that the variables are never replaced with
the real information:
(from exim log)

2002-03-13 20:21:11 16lDN9-0000Qx-00 **
|/usr/local/share/AVP/kavkeeper/kavkeeper -s ${sender_address} -r

${header_to} -m sendmail <message filter> T=virus_filter_pipe: Expansion of
"${header_to}" from command
"/usr/local/share/AVP/kavkeeper/kavkeeper -s ${sender_address} -r
${header_to} -m sendmail" in virus_filter_pipe transport failed: unknown
variable in "${header_to}"
2002-03-13 20:21:11 16lDN9-0000Qx-00 Frozen (delivery error message)


Any idea's on why variables would not be changing?


Extra info:
---CUT---
[opteq@mxhost1] /usr/local/share/AVP/kavkeeper # cat
/usr/local/etc/exim/virus-filter.exim

# Exim filter <== do not remove this line !
if not first_delivery
then
        finish
endif

pipe "/usr/local/share/AVP/kavkeeper/kavkeeper -s ${sender_address} -r
${header_to} -m sendmail"

finish

---CUT (from exim config file)---
message_filter = /usr/local/etc/exim/virus-filter.exim
message_filter_pipe_transport = virus_filter_pipe

---CUT (from exim config file)---
 virus_filter_pipe:
         driver = pipe
         return_fail_output

Thanks in advance,
Dave Raven.