kmhtConvert version 0.7 and kio_mhtml version 0.3 (and later) are able to open and display EML files. This format is used by various programs (Microsoft Outlook, Mozilla etc.) to save email messages.
Some web browsers have an option to mail the current page. This message - which contains at least one HTML document and any kind of files that were linked to the original page (images, sounds etc.) - can then be saved as EML file and viewed with kmhtConvert or kio_mhtml.
kmhtConvert and kio_mhtml can also display simple email messages (containing text and or attachments).
At this point kmhtConvert and kio_mhtml can NOT display more complex EML files, such as files originating from forwarded mail messages. These files actually contain two email messages and should be viewed with an email client.