When you send mail, you don't send it through Yahoo or Hotmail, you send it using your Internet Service Provider (ISP) servers. So, if you go to tools, accounts, and you click on one of your yahoo accounts, then go to properties, then click on the servers tab, you should have some info here. Verify your username and password first.
Look at the incoming mail and outgoing mail. Your incoming mail should be setup as the yahoo connection. But your OUTGOING mail should be your local ISP. If you are using MSN to connect to the internet, you should have something like mail.msn.com for the outgoing mail.
This might be the problem, it might not, let me know.
~Javrix
If you gave an infinate number of rednecks, an infinate number of shotguns to shoot at an infinate number of street signs, they would eventually write Romeo and Juliet in braille.