I have seen this posted in all kind of forums but never seen the answer.I have exchange installed in my server, using a public static IP address, to send and receive email. I can send to any account on yahoo, gmail or any other ISp but Hotmail. We are not listed under any list as a spammers and our firewall logs show not abnormal traffic in port 25. We have tried all solutions but none works. This is the message we get. There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <adminserver.staff.local #5.5.0 smtp;550 OU-002 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>

Hi,Apparently, the email is blocked by the Hotmail due for security policy. This is the Windows Live Hotmail issue, please refer to the below article to check this issue:http://postmaster.msn.com/Troubleshooting.aspxAdditionally, you need to access the following link to post the question on this issue if the issue persists.https://support.msn.com/eform.aspx?productKey=edfsmsbl&ct=eformtsThanksAllen