Not sure such an approach is needed. The same key used to encrypt email could be used to encrypt a search catalog. The user decrypts the entire catalog when a s

Not sure such an approach is needed. The same key used to encrypt email could be used to encrypt a search catalog. The user decrypts the entire catalog when a search needs to be done. The risk of the catalog getting too big could be mitigated by making the indexer constrain the catalog to emails from the last 30 days or so, and making the complete catalog available offline. It can be tuned by letting users add important older emails to the catalog, and so on. It's an approach I've used with a store/forward database and worked well for me with that.