I've tried to send emails to two separate hotmail addresses today and both have bounced back as follows:

[xxx]@hotmail.com Error, ERROR_CODE :550, ERROR_CODE :SC-004 (SNT004-MC2F40) Unfortunately, messages from 74.201.84.153 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 http://mail.live.com/mail/troubleshooting.aspx#errors.

I see from the forums that this problem has occurred before.  Are you aware of it and are you acting on it?

Thanks