Please make sure that you've entered your Yahoo!
Mail address as the "From" address in your email client. You won't be
able to send mail if you've entered another address.
If you have the Norton AntiVirus email feature enabled, you might have
to do additional configuration to use Outlook or Outlook Express. For
more information, please visit the Symantec web site.
If you've tried the above steps and continue to have problems, your ISP
might not allow its users to send messages with other companies' SMTP
outgoing mail servers.
If you're unable to send email, try using port 587 when sending via
Yahoo!'s SMTP server. Here's how to make this change in Outlook:
1.From the "Tools" menu, select "Accounts."
2.Select your Yahoo! POP account and click the "Properties" button.
3.Click the "Advanced" tab.
4.Next to "Outgoing server (SMTP"), change port 25 to 587.
5.Click "Apply." Then click "OK" and "Close."