Consider that Active Directory on the Sharepoint site (in this example, nicp123.wss.test.com) has a user named Paul with the email ID paul@wss.test.com. To add the user to Web Space Server, you need to create a new user on Web Space Server with paul@wss.test.com as the email ID. Then you need to login to Web Space Server, with paul@wss.test.com as the username, and add the Sharepoint Membership Portlet to your page. The Sharepoint Membership Portlet displays the Sharepoint sites for which the user is registered.
When an email ID is defined as the Authentication Search Filter (that is when the Authentication Search Filter is mail=@email_address@), only the email ID of the user registered on Web Space Server and the email ID of the user in the Active Directory on the Sharepoint site need to match. Any other user information and the password are not required to be identical.