[Exim] .forward syntax

Hi,

I would like to launch a pipe command in my .forward file for each
message and then forward message to other users if the script used in
pipe command accepts the mail.
I tried the following thing :
.forward :

"|my_command"
user1
user2
..

but unfortunately, every user is seeing all the messages that is
coming, how to set it up in a good way ?
Bye
steph