I was motivated by this list to stop depending so much on google. But it's harder than it seems. For example, if you purchase a fastmail account, you still need a google account to install the app in your non-google phone, because fastmail only provides the apk files via the google play store. There's so many such "roadblocks" in de-googlification that you inevitably give up at some point.
PSA: Fairmail is fantastic, IMO, but be aware the settings are a bit of a paradox of choice. You can customize damn near every field, font, card, and style in the app... but that's a bit overwhelming at first.
Fastmail has been working on an alternative api called jmap for ages which should modernise 3rd party clients. but as far as I’m aware they haven’t released it for real use and there are no clients.
Its been released & in use for years. (Nearly a decade at this point?).
The problem is all the big email providers - Apple Mail, GMail and Outlook haven't added support. Its a bit of a chicken and egg problem - there's no demand for jmap clients because so few servers support it. And there's no pressure on email servers to implement jmap because so few clients support it.
Source: Friends with some of the JMAP authors.
and there's a couple of client & server implementations https://jmap.io/software.html
but it's a long long way from popular yet AFAICT from the lack of support from the big hosted mail providers other than fastmail.
Do you mean that with an IMAP client you can't edit your server side Fastmail filters?
If so, a workaround is to use their web-based email client when you want to edit your filters.
Both types of anonymous session timed out repeatedly over a period of about three days so I eventually caved and made a throwaway Google account for it. In which case I should have just used the Play store.
If your explicit goal is to have a modern phone without Google specifically, you really should consider Apple.
Apple is much worse, I don't consider it a viable option. I was gifted an ipad recently, but couldn't use it without even entering my phone number (!). This is a ridiculous level of invasion that I'm not willing to put up with.