cannot send email

hi
i have an account on exchange server on our server in the company, i tried to send many mails but i failed, and got this message...
usually i can receive any incoming emails and i can send emails within the compny  but i cannot send to  to outside...
thanks
klay

Subj:	hello
 Sent:	2008-04-28 16:37
 
has encountered a delivery problem.
 
 
Reason: Bad sender's system address
The sender's system specified in the address does not exist or is incapable of accepting return mail.
This means the address portion to the right of the @ is invalid.
 
Transcript of session:
MAIL FROM:<name@company.com> SIZE=3011 550 DY-001 Mail rejected by Windows Live Hotmail for policy reasons. We generally do not accept email from dynamic IP's as they are not typically used to deliver unauthenticated SMTP e-mail to an Internet mail server. http://www.spamhaus.org maintains lists of dynamic and residential IP addresses. 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

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