[exim] Disable Bounce Messages

I have the following router . If a user is not known at our domain it's
rejected . But then in the exim queue there are a bunch of frozen bounce
messages from Mailer-Daemon@???.
How can I disable that ? Thank you all in advance.

begin routers
reject_bad:
        driver                                  = redirect
        domains                                 = +local_domains
        local_parts                             = ! 
lsearch;/etc/exim/permitted/LW-Employees-Receivers
        no_verify
        no_expn
        data                                    = :fail: $local_part not 
known at $domain
        allow_fail