Windows Live Mail
Windows 7 does not include an email program. Outlook Express is totally gone. If you were using Vista, Windows Mail is gone. As far as I know there is no place to download either of these older email programs.
However, if you have backups of Outlook Express or Windows Mail you can download Windows Live Mail and import your messages and address book (Contacts in Windows Mail), so this may be the best option for you.
When you start the install for Windows Live Mail, be sure to look at what is the default for installing.
Once you have every thing set up in Windows Live Mail and have messages and contacts, it's time to add the stored locations of those files to your backup regime.
Contacts location screenshot
Message Store Location screenshot