Proton Mail is an encrypted email service from Proton AG, aimed at individuals and organisations. It is available as a web app, as apps for iOS and Android, and as desktop apps for macOS, Windows and Linux. The service includes aliases that hide your address, scheduled sending, blocking of email trackers, and import of messages, calendars and contacts from other providers. According to Proton, zero-access encryption means the contents of your mailbox cannot be read by Proton itself; messages between Proton accounts are end-to-end encrypted, and for other recipients you can use a password or PGP.
Proton AG is headquartered in Geneva, Switzerland, and the non-profit Proton Foundation is its primary shareholder. Switzerland is not an EU member state but belongs to EFTA. Proton states that it runs its own server hardware at several locations in Switzerland and responds only to requests from Swiss authorities. It says its apps are open source and independently audited. For a European organisation, this means a Swiss provider without a US parent company.