enum havespecs (HAVE_*) -> content_info (CI_*), ++..
First try to allow the MIME parser to produce failures.
TODO After v15.0 S-nail will do
TODO
TODO - Parse MIME structure into DOM.
TODO - Analyze DOM according to desired action.
TODO I.e., modify DOM structure (e.g., explode decrypted parts),
TODO create filter chains for each part as necessary.
TODO - Walk the final DOM according to action, directly address
TODO those parts that should be addressed.
TODO
TODO - A [Dd]ecryption operation should fail when decryption
TODO fails. We need atomic operations with rollback!