After working OK, now unable to send email using Windows Live Mail on Windows 7

[David Talling]

Error message :-
The message could not be sent because the server rejected the sender's email address.
Server error 555
server smtp.ntlworld.com
Windows Live Mail Error ID:0x800ccc78
Protocol SMTP
Port 25
Secure(SSL): No

 

[americanbrian]

you have been blacklisted for sending spam. (even if you haven't sent spam personally) it happens sometimes. Has your account been hacked recently by chance?