iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Bitdefender BOX - Bitdefender BOX protects all devices connected to the Internet.
Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
ZingBox - ZingBox provides real-time IoT security solution to protect from cyber and insider threats.
mailcow - An open source mailserver suite.
Bastille - Bastille provides comprehensive visibility and threat detection for IoT devices.