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

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.

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

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

Virtru - Virtru is your data privacy force field, wrapping and protecting emails and files wherever they're shared. Easy-to-use data security software for business. People also askIs Virtru Hipaa compliant?