[exim] open or not? smtp auth against PAM: no error!

Hi,

I just setup a server with an smtp auth against PAM, on Debian Sarge.
I mostly followed
http://www.abassett.org/wiki/index.php?title=Exim4_and_smtp_auth_on_Debian

I added the /etc/pam.d/exim with the adviced content
I also filled the noauth file
then, I left commented the "plain_server" and "login_server" section, but
appended just this:

plain_server:
       driver = plaintext
       public_name = PLAIN
       server_condition = "${if pam {$1:$2}{yes}{no}}"
       server_set_id = $2
       server_prompts = :

login_server:
       driver = plaintext
       public_name = LOGIN
       server_prompts = "Username:: : Password::"
       server_condition = "${if pam {$1:$2}{yes}{no}}"
       server_set_id = $1

Ok. The auth system is OK: When I try to send an email, i am prompted for
login and password. If I provide correct login/pass, the email is
transported. The recipient receives it.
The real problem, is when I provide false login/pass, there is not error
returned, but the email does not get to the recepient mailbox.
When I provide false login/pass, the mainlog says "Completed". But the message
never get to the recepient.
How should I modify the configuration to have the error when wrong password?