Google's biggest trick has been convincing people that "search" is something that is much too hard and sophisticated to do locally. see https://notmuchmail.org

Google's biggest trick has been convincing people that "search" is something that is much too hard and sophisticated to do locally. see https://notmuchmail.org/ https://notmuchmail.org/ your email archive just isn't that big as for natural language processing, I'm not aware that Gmail does this for user search? maybe it does, but I haven't noticed more than some basic stemming. and given the choice (is not hidden), even most basic users prefer exact/stemmed keyword search over "cleverly" second-guessing returning noise results you didn't ask for. also there's many non-proprietary search result sorting and filtering techniques that do a great (and predictable!) job, locally, without having to go all deeplearning about it. remember that a lot of the sophisticated NLP analysis stuff Gmail does, is for the benefit of targeted advertising first and user experience second.