[Dovecot] Mail client kill imap-login process

[dovecot acc]

Hi,
In my env we have quite a number of old PC which are running windows95.  I
have installed the thunderbird
and outlook97 with the right configuration to dovecot.  Everytime I starts
the mail client it shows the following,
dovecot: Oct 09 10:56:45 Info: imap-login: Disconnected: rip=172.24.65.60,
lip=172.24.66.24
only then it shows the login screen.  After submit the password, it doesn't
seems to login properly.
If I use the Outlook Express, it runs ok on the same machine? I can send and
read email.

I trace the process using strace but it failed since the pid got killed
everytime I starts that two mail client.

In order to make sure my dovecot run correctly, I run all mail clients from
XP and it works like charm.

Can someone share with my what should I do next or how to debug further?
Thanks.