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.
Spark Mail - Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest. Spark for Teams allows you to create, discuss, and share email with your colleagues
dmarcian - Safeguard your email from abuse
Newton Mail - Newton is a fully featured mail client available for Android, iOS, macOS and Windows.
Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.
Aqua Mail - Android Mail Client.