I replied to one of your emails of a week or so ago and it was refused. Message said:

Unfortunately, messages from 209.17.115.110 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

Any idea what this means?

I just updated my Norton Antivirus program but that shouldn't affect email.