The message could not be sent. The authentication setting might not be correct for your outgoing e-mail [SMTP] server. For help solving this problem, go to Help, search for "Troubleshoot Windows Mail", and read the "I'm having problems sending e-mail" section. If you need help determining the proper server settings, please contact your e-mail service provider.
The rejected e-mail address was 'firstname.lastname@example.org'. Subject 'email problems and research paper', Account: 'mail.comcast.net', Server: 'smtp.comcast.net', Protocol: SMTP, Server Response: '550 5.1.0 Authentication required', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC78