Whenever our company sends out ebills or online payment receipts to customers with Hotmail accounts we receive the following rejection notice.

SNT0-MC2-F18.Snt0.hotmail.com rejected your message to the following e-mail addresses:

'USERNAME' (*** Email address is removed for privacy ***) <mailto:*** Email address is removed for privacy ***>

SNT0-MC2-F18.Snt0.hotmail.com gave this error:
SC-002 (SNT0-MC2-F18) Unfortunately, messages from 74.122.18.39 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.

I have checked all the blacklists and there are no listed IP addresses in the 74.122.18.x\24 range.  My ISP (TIme Warner) has no clue as to any communication being blocked.  Any idea what is going on?