[Exim] specific router question

and for previous questions. i store bad networks in
sql table, the 'net' field contain network showed as 'x.x.x.x/24'.
something needed in configuration:

.......

accept condition = $if{...$sender_host_address....${lookup \
mysql{select net from bad_sender}}...}
       delay 10s

.......

but ofcose, select by $sender_host_address do not work for network
stored in table is anyone knowing right way?

?

vlad.