ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
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.
HEY - Email at its best, new from Basecamp.
GPGMail - GPGMail is an open source plugin for Apple Mail.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.