My wife has been getting bounce backs via Orcon to Hotmail / Outlook.com addresses.

I have just tried from Orcon's  webmail page and get the same problem

"The original message was received at Wed, 2 Jan 2013 09:04:47 +1300
from mx5.orcon.net.nz [219.88.242.55]

----- The following addresses had permanent fatal errors -----
<xxxxxx@hotmail.com>
(reason: 550 SC-001 (COL0-MC1-F27) Unfortunately, messages from 60.234.4.74 weren't sent. Please contact your...ock list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.)

----- Transcript of session follows -----
... while talking to mx2.hotmail.com.:
>>> MAIL From:<xxxxx@orcon.net.nz> SIZE=1743
<<< 550 SC-001 (COL0-MC1-F27) Unfortunately, messages from 60.234.4.74 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.
554 5.0.0 Service unavailable"