If you referring to Yahoo ID it can be done with options available with one of Yahoo’s unoficial chat clients called YahElite (http://www.yahelite.co.uk/deep/yahelite/ ). In YahElite go to: Toys, Who is, fill up information, put asterix for unknown part. Still by looking IDs you wont be able to tell are those main Yahoo IDs or aliases. Main Yahoo ID can have up to 5 aliases which can be whatever and mail addres to them all would be: main_Yahoo_ID@yahoo.com