Tuta Mail

Tuta Mail is the email product of Tutao GmbH, headquartered in Hanover, Germany. All mail content, including subjects, bodies, attachments, calendars and contacts, is end-to-end encrypted on-device using the company's TutaCrypt protocol with post-quantum cryptography. Apps are available for iOS, Android, Windows, macOS and Linux, plus a webmail client. There is a free 1 GB plan, paid personal plans from EUR 3/month and business plans from EUR 6/month. The clients are open source.