If your problem is sending emails from your Yahoo email address via Outlook, try this:

1) Delete the problem account on Outlook

2) Set up a new Yahoo account (with the identical username & password) on Outlook:

a) use "plus.pop.mail.yahoo.com" and "plus.smtp.mail.yahoo.com" per instructions on Yahoo help pages;

b) in More Settings/Advanced, uncheck both the SSL boxes and set POP to 110 and SMTP to 25 (port numbers);

c) save those settings, shut down Outlook and re-start.

This worked for me on Outlook 2002. It may work on other versions of Outlook and other email clients. Good luck!