[Exim] perl and mysql in domain list

i store host_reject list in mysql database.

host_reject=mysql; select host from hostrejecttable where host='$key'

my concern is that when mysql query fails for any reason exim fails smtp
connection. i can't afford my mail system to depend so heavily on
avialability of mysql server. i am looking for a solution where mysql query
failure would be equivalent to SELECT returning no match.

I know that exim manual explains this problem and warns against using mysql
lookups in critical parts of config. but i was hoping that someone has found
a workaround.

i am thinking of replacing direct mysql query with a perl wrapper script so
that the script could screen lookup errors. but i can't figure out what
would be the right syntax to make the script be called from within
host_reject domain list.

Thank you,
--

Alex Petrov