[exim] Discarding external e-mails sent to our local Mailer-…

To try to discard any e-mails from the outside world sent to our local
Mailer-Daemon account I have the following in the acl_smtp_rcpt ACL
section of the Exim configuration file:

   discard hosts  =  +Company_relays
       condition  =  ${if match {$local_part} {\N(Mailer-Daemon)\N}}
       logwrite   =  External e-mail from '$sender_address' for
'Mailer-Daemon' - discard!

This code is meant to check e-mails that have come through our company's
relay from the outside world and reject it if it is sent to
Mailer-Daemon.

It doesn't seem to be working as I am getting occasional e-mails
delivered to Mailer-Daemon (i.e. me).


Any ideas of how I can code this to achieve what I am after?



Thanks


Paul McIlfatrick