I've recently been thinking about Roundcube's handling of message/rfc822 attachments. The current behavior is that message/rfc822 parts are 'flattened': content parts are appended to the main message body, honoring text or HTML alternative preferences; file attachments listed in the header section with no indication that they are a sub-attachment; a link is provided to download entire message part in raw format.
Most mail clients handle the message/rfc822 part as single attachment that's natively viewable in a self-contained format. Double-clicking or otherwise activating the attachment opens it for viewing just like a message pulled down directly from the IMAP server. This is what I'd like Roundcube to do as well.
As far as I can tell, this would require some fairly in-depth changes to the core logic. One approach would be to extend or subclass rcube_message to support message/rfc822 parts, and update some code that that refers to messages by uid to support uid+part selectors. There would also need to be some changes to the UI and possibly the skin layout to support navigation through message parts.
I'm glad to take this on, but I thought I'd run it past folks first to see if there's any support for or objections against this effort.
-Brad
List info: http://lists.roundcube.net/dev/