Our group at Harvard University is not able send mail to hotmail accounts 
(including mine),  all our messages are being rejected with the following 
message. Our going mail is coming  from the harvard.edu domain, perhaps 
from ackroyd.harvard.edu. This was working fine until very recently.

Please change things back to allow our domain to send mail to hotmail accounts.

host mx2.hotmail.com[65.55.37.104] said: 550 SC-001
    Mail rejected by Windows Live Hotmail for policy reasons. Reasons for
    rejection may be related to content with spam-like characteristics or
    IP/domain reputation problems. 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)

Hi harvard guy.

I've escalated your issue to our Windows Live Hotmail Sender Support Team. To accelerate the resolution of the issue, please ask your domain admin to http://postmaster.live.com and review our policies and guidelines. You may also post their contact e-mail address so that our Windows Live Hotmail Sender Support Team will contact them directly.

We have made changes on our end that seems to have fixed the problem.

Thanks.