Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Riseup - Riseup provides online communication tools for people and groups working on liberatory social change. We are a project to create democratic alternatives and practice self-determination by controlling our own secure means of communications.
eM Client - eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.
Posteo - Web- and IMAP-based email service. 2GB cost 1€/month.