Windows: If you ave some old emails you'd like to retrieve from Windows Live, Outlook Express or Thunderbird, Mailviewer can do so — no installation required.
Mailviewer can view email databases from Outlook Express, Windows Vista Mail, Windows Live Mail and Thunderbird. Just open it up, browse to your mail database, and you'll be able to see your messages as well as search or extract individual ones.
The best part? It's completely portable, so you don't need to install anything. Hit the link to check it out.