As mails bounch around some email programs (I’m looking at you, Microsoft), seems to encrypt package forwarded mails in attachments with the extension .eml.
While Mozilla Thunderbird should be able to read them (as should Evolution), it requires you have the mail application available on your machine, but I haven’t - I’m doing just fine with GMail in the browser. So far the best solution I’ve find - assuming it’s trivial non-sensitive, personal files - that an Online viewer seems to work pretty well. My preferred solution is the free one from encryptomatic. It handles the mails quite nicely, it restores the formatting to something quite readable and even handles embedded images and attachments within the eml-file.
If you’re using Windows Live Mail or any other mail application running on windows, it can probably handle the .eml files. An other option is to look for an App, as there seems to exist several apps on windows, which renders the .eml files with no issues.
A little trick (with a browser)
When using windows - even in a VirtualBox - there’s an easy little trick you can use: Save the file and simply rename the file extension from “.eml” to “.mht” and open the file with Internet Explorer. It should render perfectly.
Once the .eml file is renamed to .mht Google Chrome and Firefox seems able to render the contents too - though handling images and attachments seems much less graceful.