Hi, Jenk,
According to this page, there's an easy way and a hard way. I would go with the easy way - type a hyphen at the beginning of every email address. Now, if you have hundreds of addresses already entered (or even just 20), the easiest way to change all of them that I know of is to change the first one, tab down to the next address and type Ctrl-Y, which means "do what I just did to the last field." So one hand presses the down arrow and the other hand stretches to do Ctrl-Y. It's quite fast and easy, especially if you ever played a keyboard.