[Exim] Exim and outlook / outlook express

Hello,
I have a trouble with outlook and outlook express :

When I want to use Exim to send a message, with some outlook
(97/2000/express) it
works very easily. But with some others, I have trouble and the main log of
exim is :


SMTP data timeout (message abandoned) on connection from (toto)
[195.6.28.22]

Does someone knows this trouble?

Thanks for your help.
Christophe from the sunny Chambery.