Exim - small routing issue (catch-all to nonexistant local mailbox)

When a customer sets their catch-all ('Default Address') to a non-existant local email address eg. shsyussk@customerdomain.com and all mail that is sent to non existant mailboxes on this domain gets re-routed to 'postmaster' because Exim isn't able to find the catch-all..

Is there any way to change this behaviour so that even if the catch-all doesn't exist, the mail is discarded and not rerouted to postmaster/root ?

 

Just a couple of notes ... I've noticed that cpanel won't let you set your catch-all to a non-existant local mailbox BUT if you set up a catch-all and then later remove the mailbox then you end up in the situation I described above ie. catch-all pointing to non existant local mailbox and hence rerouting of all unrouted mail to postmaster.