How can I forward email as a readable attachment? I'm writing a new email, and in that email I'm referring to a couple of other emails and I want to include them as attachments. When I drag and drop a mail to the mail I'm writing, some icon appears but when I double click on it, it shows plain text with headers, and not a nice formatted mail.

How can I attach it properly?

ATTENTION!! I know about "Mail -> Message -> Forward as Attachment" but it is not working properly: when I double-click on attached icon, it opens as text (with headers) and not as nice formatted mail. I also know about "Save as RTF" - but this is also not a proper solution as headers are lost.

For example, when I attach email in Thunderbird or Outlook, it attaches EML file - and when I open it, it is displayed properly (with formatting), and it is also has all headers (but not visible by default).

OS X 10.9, Mail 7.0 (1816)
If you find the message in Library->Mail copy the .emlx file into the email then you will be able to see it nicely in mail (worked for me).

Unfortunately, the challenge here would be to find the message that you want to send (since the file categories seem arbitrary, at least to me).