how can I resolve this isue of mail being rejected when I send to hotmail users from my mail server?

COL0-MC4-F32.Col0.hotmail.com rejected your message to the following e-mail addresses:

*** Email address is removed for privacy *** (*** Email address is removed for privacy ***)

COL0-MC4-F32.Col0.hotmail.com gave this error:
SC-001 (COL0-MC4-F32) Unfortunately, messages from 41.215.180.61 weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.

A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.

Diagnostic information for administrators:

Generating server: nao-server06.nao.local

*** Email address is removed for privacy ***
COL0-MC4-F32.Col0.hotmail.com #550 SC-001 (COL0-MC4-F32) Unfortunately, messages from 41.215.180.61 weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. ##

Original message headers:

Received: from nao-server06.nao.local ([::1]) by nao-server06.nao.local
 ([::1]) with mapi id 14.01.0421.002; Tue, 27 Nov 2012 10:51:44 +0200
From: Wesley Kachali <*** Email address is removed for privacy ***>
To: "*** Email address is removed for privacy ***" <*** Email address is removed for privacy ***>
Subject: test
Thread-Topic: test
Thread-Index: Ac3MfCRZb39SPAZTSw231VvzW1stgg==
Date: Tue, 27 Nov 2012 08:49:41 +0000
Message-ID: <*** Email address is removed for privacy ***>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-originating-ip: [192.168.16.100]
Content-Type: multipart/alternative;
            boundary="_000_775EE516960EDA41A1C08CA3F112F102011527A7naoserver06naol_"
MIME-Version: 1.0