[exim] Transport_filter and first delivery

I have been messing around with the transport filter facility for a bit
and am having trouble with proper usage of the first_delivery
condition, I realize it is common to use it in system filters but I
haven't found any solid examples where first_delivery is in the
transport_filter line. Currently my transport filter line looks like this:

transport_filter = /bin/el_dksign -o /etc/el_dksign.conf -d
${authenticated_id} -r "${if first_delivery {-l/var/log/el_dksign.log}{}}"

the probem i am having is that when a message fails to be delivered like
this

2005-05-13 14:41:30 1DWg2L-0003bV-6q <= user@??? ....S=334 from ...
for ....
2005-05-13 14:41:30 1DWg2L-0003bV-6q Remote host mx2.mail.yahoo.com
[4.79.181.13] closed connection in response to end of data
2005-05-13 14:41:33 1DWg23-0003bN-S3 mx1.mail.yahoo.com [4.79.181.12]:
Connection timed out

it gets immediatly retried?? (isn't this the second delivery attempt?)

2005-05-13 14:41:34 1DWg2L-0003bV-6q => .... R=dnslookup T=remote_smtp
S=525 H=mx2.mail.yahoo.com [67.28.114.35] C="250 ok dirdel"
2005-05-13 14:41:34 1DWg2L-0003bV-6q Completed

and is delivered. Now the external program that I use in the
transport_filter has a seperate logfile (the -l option), and I only want
to log once for that message, I thought the first_delivery condition
would fix that but it still logged it twice. So am I misunderstanding
the usage of first_delivery?

anyone have any suggestions?


Tim