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: 553
Server Response: 553 Authentication is required to send mail as <*** Email address is removed for privacy ***>
Server: 'smtp.suddenlink.net'
Windows Live Mail Error ID: 0x800CCC78
Protocol: SMTP
Port: 25
Secure(SSL): No

[Original title: I have Windows Live Mail 2015 and it won't let me send emails. This is the error message I get:]