emails remain in my out box

[Joe@Yahoo]

I set up Outlook with my yahoo email. I can receive emails but when I send
they remain in my out box. I have the Outgoing mail server(SMTP) defined as
smtp.mail.yahoo.net. I also selected the authentication check box. I clicked
Use same settings as my incoming mail server. Any ideas of what may be
happening or what I forgot to do?

Thanks