[exim] I can't completely rewrite the from field

Hello,

I use exim4 in a debian testing.
The rewrite method with an /etc/email-addresses work almost fine.
The mail start but I want to change the outside from field :

The loggin is fmy or root
The /etc/email-addresses is
fmy: xxxx@yyyy
root: xxxx@yyyy
The message go to xxxx@yyyy with this from field :
fmy <xxxx@yyyy>
or root <xxx@yyyy>

I want to send only xxxx@yyyy and remove or change the login name.
How can I do ?

Thanks.

Francois