SASL with Postfix

I have installed SASL & Postfix for SMTP auth, it is working fine in some of the mail clients(Netscape) but it is not working in some of the mail clients(Microsoft Clients).

We need to change settings in Non working Mail clients, that is to say my SMTP needs Auth. But if the user removes the specifed settings in the mail clients it wont prompt for Auth. Any solution?