It appears that most/all hotmail accounts were placed on
"bouncing" status by Yahoo within the last few days.
Here's info on resetting a bouncing account:
http://help.yahoo.com/help/us/groups/messages/messages-08.html
1. Go to the My Groups page.
http://groups.yahoo.com/mygroups
2. If you notice a bounce alert near the top of the page, click
on the link. This will take you to the My Preferences page.
3. Click on the Reset link.
vpFREE Administrator