OT:Can not send email.

I posted this question earlier but after checking more on the forum, someone stated to post the entire error message.  I downloaded Live Mail in August when I got a new computer with windows 8.1.  Everything worked fine until several weeks ago when outgoing emails stopped sending and the error below was given.  I have uninstalled Live Mail and deleted all my contacts and then reinstalled Live Mail and hand typed my contacts into the program. I still can not send emails and receive this error message.

An unknown error was returned from the SMTP server.

Subject 'test'
Server Error: 521
Server Response: 521 This system is configured to reject mail from 199.187.253.145
Server: ************
Windows Live Mail Error ID: 0x800CCC61
Protocol: SMTP
Port: 25
Secure(SSL): No

I have no idea how to fix this and am not knowledgeable with computers.  I thank you for any help.