IsLoginValid(Microsoft.SharePoint.SPSite, String) Method
The IsLoginValid method of the SPUtility class uses the specified site collection to determine whether the specified user name is valid.
Parameters
site A Microsoft.SharePoint.SPSite object that represents the site.
strLoginName A string that contains the user name.
Return Value
true if the user name is valid; otherwise, false.
Requirements
Platforms: Microsoft Windows Server 2003
Security: Code Access Security