[Exim] received_header.

Expansions, especially long, nested expansions are not my strong
point;)

v3.22

I am trying to modify the default received_header string, to omit the
sender_rcvhost information, only when the sender is authenticated (SMTP
AUTH is already setup and working ok, and I've got an appropriate
server_set_id included. When it does this I would like the auth ID to
show instead..

Can anyone help me write the expansion properly?