CSS not working properly for Emails in HTML format

Question

Hi,
I am developing an application in which we are sending system generated emails in html format. Following are the details:
Application details - .Net 2.0 , Web Application in C#
Problem summary:
I am creating the html mail format using a string builder . I am applying inline CSS. when this html renders on the web browser all the CSS that is applied, shows correctly.
But when this same HTML is viewed in the mail clients (eg: Lotus Notes ,Outlook etc.) CSS breaks.
The users of my application use Lotus Notes 6/7, and CSS borders dont show in these. Please suggest a workaround as I need borders implemented for these mails and particularly for Lotus Notes 6/7 .
Thanks in advance