the only time your going to use yahoo is if your portal is yahoo if its not and just verizon it will be incoming.verizon.net and outgoing.verizon.net. The outgoing server does require Authentication and just use the same as the incoming server.
Not sure what you mean by "if your portal is yahoo". Mail.app is like any other desktop mail client - Eudora, Outlook, etc. I was able to edit an old account and everything is working correctly now.
Some users have the Verizon Yahoo mail option. If you have the firstname.lastname@example.org like me, then it is as stated by Techman28.