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free and open-source end-to-end encrypted email software and host

Roundcube is a web-based IMAP email client written in PHP. It uses Ajax throughout its interface and is licensed under the GNU GPL version 3 or later, with exceptions for skins and plugins.

SquirrelMail is an open-source webmail application written in PHP. It provides a web-based interface for accessing email via the IMAP protocol and sends messages through SMTP. The project also includes a separate IMAP proxy server written in C. Both components are released under the GNU General Public License version 2 or later.