I use also Murena Mail, apart of Proton https://murena.io
Murena is a whole ecosystem, similar to GDrive, they even had launched the complete degoogled Murena smartphones
Tech Radar review
Murena’s key goal is to stop companies collecting unnecessary data from your phone and online footprints, which it says accounts for up to 12Mb every single day. Transparency is clearly important when browsing Murena’s website, which states that all of its servers are based in Europe including its Finnish email and cloud servers, resulting in full GDPR compliance.
Nextcloud, which sets the foundation for many of Murena’s services, is end-to-end encrypted, while a statement on Murena’s website reads:
“We don’t scan your data, we don’t log your app usage, we don’t sell your data, we don’t use ads in our online services.”
Negative points for some
Only 1 GB Cloud for free (maybe enough if you only use the mail)
Somewhat more expensive than others with the Premium plan