I am using Outlook Express and this morning have tried to send emails to Hotmail and MSN accounts and they have come right back with this message

The reason for the problem:
5.1.0 - Unknown address error 550-"SC-004 (SNT0-MC3-F4) Unfortunately, messages from 212.74.100.45 weren't sent. We recommend that you contact your Internet service provider. The problem is that too many unwanted messages have been sent from the following IP address above. You can also refer your provider to Troubleshooting

I'v refered to the link they have given and I get this

Mail rejected by Windows Live Hotmail for policy reasons. A block has been placed against your IP address because we have received complaints concerning mail coming from that IP address. We recommend enrolling in our Junk Email Reporting Program (JMRP), a free program intended to help senders remove unwanted recipients from their email list. If you are not an email/network admin please contact your Email/Internet Service Provider for help.

Had a look on line and it seems to have been a problem last year as I read on a forum but no one seems to know how to correct the issue.

Can anyone here help, trying to get through to my internet provider is a nightmare and costs a fortune per min to call!!