how dynamically to create folder on server

            if (!Directory.Exists(Server.MapPath(@"~/Email/"))) 
            {
                Directory.CreateDirectory(Server.MapPath(@"~/Email/"));
            }

irrespective to the task u can create the folder by above code.

Mail is not a file that you can move to some folder. Kindly elaborate what you are upto and how are you reading emails.

Are you using some email server like GMAIL?