[exim] Redirect with mysql

Hi,
I'm doing an exim install to replace a legacy email system where all subscribers are doing an external redirectI used the following rule as conf.d/router/120_CPD_client_aliases
client_aliases:    debug_print = "R: client_aliases_XXX for $local_part@$domain"    driver = redirect    domains =  +local_domains    data = ${lookup mysql{SELECT real_address FROM client_aliases2 WHERE local_part='${sg{$local_part}{'}{''}}' AND local_domain='$domain'}}


The rule is working but I would like the emails sent to addresses that do not exist in the table to be discarded.
Does anyone have any ideas?



really appreciate your help
Luciano,