I've been using the Outlook app on iOS and still prefer using Gmail from my web browser on Windows (desktop). My default mailto: goes to the Outlook app. I'm fine with that. The types of customer service email that start there I don't want coming back to my Gmail as a bunch of spam follow ups and "rate our customer service" requests or spam from my address getting sold.
Definitely not the new Mail app of Windows 10. Man, what a disaster. Don't understand why MS not used the 'old' Mail app of Windows 8/8.1. It was not good, but a lot better than this one. Read the reviews in the Store.
Thunderbird (which I started using many Windows versions ago) is still working well for me on Windows 10. Thunderbird's search features let me use my email as a database to find all sorts of stuff, current and past. I think Thunderbird makes it easy to control where my email is stored. I recently posted a message that explains how I migrated Thunderbird data to Windows 10, posted at the end of the following thread: How to copy your Mozilla Thunderbird email profile to a new computer