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.
DistroWatch - 9 hours ago - It does include a proprietary software set optimized for business users, students, researchers and developers." A list of features and further details can be found in the company's release announcement.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
SUSE Studio - Modernisieren Sie Ihre Infrastruktur mit SUSE Linux Enterprise Server, OpenStack Cloud-Technologie für IAAS und softwaredefiniertem Storage von SUSE.
mailcow - An open source mailserver suite.
Puppy Linux - Home, overview and getting started with Puppy Linux, amazingly fast, fascinatingly complete and delightfully small Linux.Wiki · Download latest Puppy Linux .