[Exim] Help sending from exim to Exchange relay

Hi

I am running exim 3.22-4 on a Linux box (debian 2.2r2).
I am reading my mails with elm.

All my mail needs to be sent to an exchange server where
I do have an account.

If I try to send a message using netscape mail, it prompts
me for a password for the SMTP server (thus the exchange server)
and sends the message.

If I want to send a message from elm, it talks to my local
SMTP daemon (exim) that connects correctly to the exchange server
but I get a error message saying that relaying is prohibited:

2001-04-19 10:51:09 14qA9d-0000Pv-00 <= jn.colin@??? U=jnc
P=local S=477
2001-04-19 10:51:14 14qA9d-0000Pv-00 ** jnc@??? R=smarthost
T=remote_smtp: SMTP error from remote mailer after RCPT
TO:<jnc@???>: host exchange.tradeware.be [192.168.2.249]: 550
Relaying is prohibited
2001-04-19 10:51:14 14qA9i-0000Q0-00 <= <> R=14qA9d-0000Pv-00 U=mail
P=local S=1359
2001-04-19 10:51:14 14qA9d-0000Pv-00 Error message sent to
jn.colin@???
2001-04-19 10:51:14 14qA9d-0000Pv-00 Completed
2001-04-19 10:51:18 14qA9i-0000Q0-00 => jn.colin@???
R=smarthost T=remote_smtp H=exchange.tradeware.be
2001-04-19 10:51:18 14qA9i-0000Q0-00 Completed

Apparently, it is an authentication problem. If I run EHLO on the
Exchange server, I get the following:
250-XEXCH50
250-HELP
250-ETRN
250-DSN
250-SIZE 0
250-AUTH LOGIN
250 AUTH=LOGIN

So I added a auth section to my exim file

jnc@strider:~$ /usr/sbin/exim -bP authenticators

fixed_login authenticator:
driver = plaintext
public_name = LOGIN
server_mail_auth_condition =
server_set_id =
client_send = : test : test
server_condition =
server_prompts =

But it still does not work.

Can someone help me?

Thanks a lot

Jean-Noel