How do I edit a text file email list?

I have a list of emails that I need to send a newsletter to. The list I have has a space in between each email address. The program I will be using to send the email needs to have the emails listed with one email per line like this: "johndoe@hotmail.com janedoe@yahoo.com,,, " Andi I need it to list then one per line. The file i am using is a text file. Notepad has no way to m edit the list the way I need to. Anybody have any suggestions on how I can quickly edit this .txt file?