OneCare is not an email program, so I'm not sure what you are looking for.
OneCare - http://onecare.live.com
If you are referring to Hotmail, just upgraded on the web for your account, the mail is on the Hotmail servers, not on your PC unless you are using an email program such as Windows Live Mail to access your Hotmail account.
If you do mean OneCare and want to restore old emails from a backup, please post a new message in the Backup topic folder and explain more details about the program you are using for email and what it is that you are trying to do.
-steve