Returned Type: 
UserCheckMailResult
Returns a UserCheckMailResult object that has the following structure:
    
    
        
            | int <ispresent> | can be: 0 (zero) mail address does not exist, 1 (one) mail address exists but the corresponding user has not been activated, 2 (two) mail address exists and the corresponding user has been activated, 3 (three) mail address exists, the corresponding user has been activated but also blocked because of too many attempts to login with wrong password | 
        
            | string <UserName> | if mail address exists, this contain the user's username |