Proofpoint VS Mailguard

Mimecast Gateway - Mimecast Gateway is a SaaS-based email security solution that uses sophisticated, multi-layered detection engines and intelligence to protect email data and employees from malware, spam, advanced threats and zero-day attacks.

dmarcian - Safeguard your email from abuse

Barracuda Email Protection - Barracuda Essentials offers advanced Office 365 security features including email scanning, archiving, backup & recovery, and real-time phishing defense.

Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.

Symantec Email Security.cloud - Symantec Email Security.cloud provides always-on, inbound and outbound email security against malware, targeted attacks, and advanced threats

Securence - Securence is a managed spam service offering anti-spam and anti-virus filtering technologies.