Dano,
A lot of the web based e-mail accounts have changed in the last year so that you must check them monthly or your account will go away. Also with that they changed how long the messages might stay around in your in basket. If you have a computer I would suggest saving the messages locally to your computer. You can save the addresses too just to make sure you have them. Once they are gone from the mail in Yahoo there is really no way to get them back.
Yahoo used to forward its messages for free to another e-mail (like a POP3) but now they charge for that service. HotMail never offered that feature (it was nice while it lasted).
Hope this helps.
- Brian