Can't send email to hotmail only

Guys,

Pls, any suggestion will be higly appreciated, users cant send email on Hotmail only, the error is attach below.

"The following mail could not be delivered

Failed recipient(s):

mra99@hotmail.com

Error message:

550 SC-002 Mail rejected by Windows Live Hotmail for policy reasons. The mail server IP connecting to Windows Live Hotmail has exhibited namespace mining behavior. If you are not an email/network admin please contact your E-mail/Internet Service Provider for help. Email/network admins, please visit http://postmaster.live.com for email delivery information and support"

Subject: Can’t send email to hotmail only

550 DY-002 Mail rejected by Windows Live Hotmail for policy reasons. The likely cause is a compromised or virus infected server/personal computer. If you are not an e-mail/network admin please contact your E-mail/Internet Service Provider for help.

Subject: Can’t send email to hotmail only

try to contact windows live and let the Sender Escalation team sort things out.It will depend on your sysadmin how many time he has to resolve this.