I solved my email problem in a few ways. First I make my email subject line detailed so I can easily find it again when searching.

Second, I treat my emails as disposable. If something is really important I save the email as a PDF to Google Drive and/or OneDrive. Both can search the contents of a PDF. I also avoid attaching files but send links to the files. OneDrive fixed their links and now it is on par with Google.

Lastly I make use of functions like Gmail Snooze so the email reappears when I need to perform a task.

Just in case you haven't, you should look at the entire history of Superhuman (which just got bought by Grammarly this past week).

You can even start here -> https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...

gmail does a great job of sorting emails into catagories plus if you master filters and after I made a dozen, it's easy to manage tons of email coming in I think also gmail is easy to unsubscribe from lists or mark stuff as spam