To Setup a Yahoo Email account in Outlook, you must use IMAP.
The Incoming server is imap.mail.yahoo.com
The Outgoing server is smtp.mail.yahoo.com
In the Logon Information, use only the username, not the entire email address.
Click MORE SETTINGS.
Click the OUTGOING tab and make sure it is set to REQUIRES AUTHENTICATION and USE SAME SETTINGS AS INCOMING
Click the ADVANCED tab
The INCOMING PORT is 993 with SSL
The OUTGOING PORT is 465 with SSL