[exim] SMTP Auth cause Return-path: and Sender: to be added.…

Hi!

I'm currently using smtp authentification to send mail thrue my exim
using this config:

begin authenticators
fixed_login:
driver = plaintext
public_name = LOGIN
server_prompts = "Username:: : Password::"
server_condition = ${if and {{eq{$1}{foo}}{eq{$2}{pass}}}{yes}{no}}
server_set_id=$1


The problem is that sended email contains a "Sender:" header containg
the usernamed used for authentication:

Return-path: <foo@???>
Sender: foo@???

but the mail is sended from bill@??? using smtp auth!?

I think this is not really good cause this is the half answer of my
authentification process!

Is there a way to not include these headers when sending mail thrue auth???

Regards