Thunderbird on Windows, I have used it as far as I can think back (10+ years).
On Android currently FairEmail because the native Gmail app sucks. But it’s very much a power user app that’s a bit complicated at first, but then works like a charm (It also has a one-time purchase of $5.99 for extra features, no ads, no tracking, no data sent to the app developer).
Thunderbird on Windows, I have used it as far as I can think back (10+ years).
On Android currently FairEmail because the native Gmail app sucks. But it’s very much a power user app that’s a bit complicated at first, but then works like a charm (It also has a one-time purchase of $5.99 for extra features, no ads, no tracking, no data sent to the app developer).