Honestly i could live without fast. If its a text file there is always grep, ripgrep, silver searcher etc. But there is nothing in my deleted email demanding immediate attention. Any situation i forsee would accommodate waiting hours or days. I was kind of hoping to continue interacting with it in a webmail kind if way because piling up too many new things for something i wont be working on regularly is just asking for a mess.
The mutt/notmuch proposal is a solid solution for the right person. To me, learning like 5 new major tools just for one project is a big risk. I played around with this stuff a couple years ago and failed at creating even a simple setup to do regular mail stuff. It is absolutely not clear.
So i might try one if the intermediate solutions mentioned elsewhere. A solution that digests mail be acceptable as an addon extra.