NethServer - NethServer is an operating system for Linux enthusiasts, designed for small offices and medium...
Barracuda Email Security Gateway - Barracuda's Email Security Gateway is a powerful antivirus filter specifically designed to identify and eliminate email-borne threats, stopping hazards before they reach the network.
ClearOS - A very good alternative for Windows Server, for free
Proofpoint Email Security and Protection - Learn about Proofpoint's email security solutions that protect organizations against threats such as email fraud, phishing, spam, bulk email, and viruses.
Univention Corporate Server - Univention Corporate Server UCS with Active Directory functions and App Center is the cost-efficient and popular successor to Microsoft's server solutions.
Cisco Email Security - Cisco Email Security protects against ransomware, business email compromise, spoofing, and phishing.