The Fastmail app itself is mostly a wrapper around the web app with integrations for notifications etc. Sans notifications it works perfectly as an installed PWA on Android. Ive been using it like that for months.
Alternatively there are lots of IMAP apps available. I was testing Thunderbird for Android recently and that works pretty well too.
Disclaimer: I work for Fastmail. But any opinions I have on here are my own.
To add another example to your great post.
And when there are exceptions, they are based on the type of good. Eg in Australia GST isn’t charged on fresh fruit and vegetables in a grocery store. It doesn’t matter whether an orange was grown in Australia or internationally it will be tax free.
Whereas with a tariff, a orange grown locally will be tax exempt whereas the imported one (from a tariff applied country) will.