Sometimes people give you .msg files saved from Outlook instead of forwarding those mails by e-mail.
Opening a .msg file requires Outlook.
You don’t need to bind Outlook to an e-mail account for this (so you can skip those steps when asked the first time Outlook opens). An Office installation that includes Outlook suffices.
After opening the message:
- Open the toolbar if it’s not open yet
- Under “Move” choose “Actions” -> “Other Actions”
- Then choose either “Message Header” or “View Source”
For some HTML messages, “View Source” is not available. I’m not yet sure why.
–jeroen
via: How can I view the entire source code of an email in Outlook 2010? – Super User