windows mail+hotmail

Je suis sur Vista et utilise Windows Mail. Quand j'envoie un mail à un destinataire qui utilise hotmail.com ou hotmail.fr j'ai le message suivant:

xxx@hotmail.fr>: host mx2.hotmail.com[65.55.92.136] said: 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
(in reply to MAIL FROM command)

xxx@hotmail.com>: host mx3.hotmail.com[65.55.37.104] said: 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
(in reply to MAIL FROM command)

1.POURQUOI?
2.QUE FAIRE?

MERCI de votre aide