I'm having problems send emails from Live Mail.  No problem receiving them.  I'm running Windows 10 with Windows Live Mail 2012.

Error is -

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 'Try'
Server Error: 503
Server Response: 503 Authentication Required
Server: 'mail.bigpond.com'
Windows Live Mail Error ID: 0x800CCC78
Protocol: SMTP
Port: 25
Secure(SSL): No

Help please. 

Thanks.