http://tutacomm6oqwlbbpd246mljjxpupuxxqj2jg5mfdyegeaetdauigslad.onion/blog/first-search-encrypted-data
On top of that, Tutanota makes sure that no one but the user can read their search index. Even in the event of someone
gaining access to a person’s hard drive, they will not be able to read this person’s search
index. Consequently, the encrypted Tutanota emails remain fully secure because the search index is stored encrypted as well.