Please recommend other interesting email services by your experience.
I have switched from Google's Gmail to ProtonMail and kMail. I really like both, kMail (by Infomaniak) have very similar app interface to Gmail so you will get used to it very fast and also have big storage for free and very good offers for paid plans 👍🏼
Been using mailbox.org for a couple of years and I'm quite happy with it. Don't know what "needs client app" is supposed to mean though. If you don't want to use a mail client you can use the web interface. I've used maildroid on Android with it and when it was discontinued switched to Thunderbird, both work fine with mailbox.org.
There's one tiny minor annoyance, they somehow automatically create a new "archive" folder for every year that the web interface uses when you hit the archive button but in your mail client you gotta change the preferences manually once a year. Don't know if you can change but it's such a minor inconvenience I never bothered to check.