What's amusing is that at that very time, Google was building its Email Discovery platform (https://support.google.com/a/answer/2462365?hl=en)- basically a way for lawyers to search, inspect, and triage emails in an org to make them available. Yes, lawyers (billing hourly) trawl through hundreds to thousands of email then hand them over to the opposition. I talked to the eng building the product and they said they personally had to do some manual email classification to train the retrieval models and that they lost any interest in using email after seeing what people put it their corporate email.