Yes, this is unrelated, so I've split the topic.
Are such messages intentionally packages as attachments? I think you assume too much crypto knowledge on my part
It would be nice to get a debug log, with "raw session data" -- with the log enabled, just open the message and hit Menu -> Diag: reload, and let it complete. This way I'll be able to see how your IMAP server parses the message into parts.
