It's currently rather difficult to display the mime-part tree as it is presented because what's exported doesn't reflect what needs to be displayed.
MimeMesssgePart isAttachment CryptoMessagePart isAttachment CryptoMessagePart isAttachment TextMessagePart isAttachment MessagePart (main body) TextMessagePart isAttachment MessagePart (signed encrypted attachment) CryptoMessagePart isAttachment TextMessagePart isAttachment MessagePart (unsigned encrypted attachment)
This results in a ridiculous amount of nested views that do absolutely nothing.
Also, we can't filter out attachments, because everything that isn't directly a text part is an attachment it seems.
What we need is this:
Message Text (main body, encrypted, signed) Attachment (encrypted, signed) Attachment (encrypted)
So rather a fairly flat tree, with properties to figure out what is now signed or encrypted.
In most cases a list should be good enough, in some cases some hierarchical information may be useful to be able to display some thing inline.