To read an email sent as an attachment from another email client (e.g. Outlook) you just save the file and give it an .eml extension - then you can open it using Mozilla's Thunderbird (on Windows, Linux or OSX) - Just go to the 'File' menu and select 'Open Saved Message...'. I assume you should also be able to use Outlook on Windows.
You can just open the message in a text editor - like Gedit, Notepad, Notepad++, Textedit, etc
There are also some utilities out there to convert .eml to mbox format.