[exim] Blocking external mails to particular id

Hello,

I want to block mails from any external (non local) user from sending
mails to a system alias say mytestid on my mail server (debian, exim
4.59). I have added the following deny directive in acl_smtp_rcpt:

  deny
    message = email not allowed to this id
    !hosts = :
    recipients = mytestid

It does not seem to be working. Can somebody please help me with pointers
to the errors or documentation?

Thanks & Regards,
Biju Abraham N.