[exim] received_header_text modification

Hello all!

We are trying to modify the contents of received_header_text from:

   received_header_text = Received: \
       ${if def:sender_rcvhost {from $sender_rcvhost\n\t}\
       {${if def:sender_ident {from $sender_ident }}\
       ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
       by $primary_hostname \
       ${if def:received_protocol {with $received_protocol}} \
       ${if def:tls_cipher {($tls_cipher)\n\t}}\
       (Exim $version_number)\n\t\
       id $message_id\
       ${if def:received_for {\n\tfor $received_for}}

... to a form which can avoid tracking internal IP addresses of our
platform.
I've thought in put sender_host_name instead of sender_rcvhost to write
down server names, and to put

host_lookup = (internal range) : (internal range) : .....

but it didn't work. Exim is still stamping IP addresses. Do you know
what's wrong ?

--

    Regards,

        Manuel Molina Cuberos
        ya.com Internet Factory
        91 141 7931