What are some alternatives?
Symantec Email Security.cloud - Symantec Email Security.cloud provides always-on, inbound and outbound email security against malware, targeted attacks, and advanced threats
dmarcian - Safeguard your email from abuse
Proofpoint - Proofpoint provides cloud-based email security, e-discovery and compliance solutions for companies to protect sensitive business data.
Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.
Cisco Email Security - Cisco Email Security protects against ransomware, business email compromise, spoofing, and phishing.
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.