Since getting Windows 7 and Windows Live Mail I have been unable to send or reply to emails. Following is the error I receive, I feel sure it is the way the account is set up but I can't find the error.

The message could not be sent because the server rejected the sender's email address. The sender's email address was '*** Email address is removed for privacy ***'.

Subject 'test'
Server Error: 530
Server Response: 530 5.7.1 Authentication required
Server: 'smtp.att.yahoo.com'
Windows Live Mail Error ID: 0x800CCC78
Protocol: SMTP
Port: 465
Secure(SSL): Yes