How can I forward email as nice readable attachment? I'm writing a new email, and in that email I'm referring to a couple of other emails. In Outlook or Thunderbird I used to just drag and drop mails to my new mail and they appeared as attachments.

In OS X Mail, some icon appears in the mail but when I double click on it, it shows plain text with headers, and not a nice HTML mail.

How can I attach it properly?

OS X 10.9, Mail 7.0 (1816)
Use Mail -> Message -> Forward as Attachment to send the selected mail messages on as an attachment.