If you're using Windows online email services (Hotmail or Outlook.com), Windows 7 may store emails used with accounts accessed on the PC in the Users folder on the C drive. You should be able to find emails in the .eml format at this location:

C:\Users\[User Name]\AppData\Local\Microsoft\Windows Live Mail

There are separate folders for emails from in the inbox and the outbox. Don't miss the additional email data that is saved in the 'Storage Folders' subfolder.