Retarus is a global enterprise cloud messaging service provider specializing in secure business communications. Founded in 1992 in Germany, Retarus offers a comprehensive suite of services including email security, transactional email, fax, SMS, and EDI solutions designed for corporate environments with strict compliance and security requirements.

As an ESP, Retarus provides Email for Applications services that enable businesses to send transactional and marketing emails with high deliverability rates. While not primarily focused on creative template building like marketing-oriented ESPs, Retarus offers email template management capabilities within its Enterprise Email Service that support HTML formats and personalization for business communications.

Retarus distinguishes itself through its emphasis on security, compliance, and reliability for mission-critical business communications. The platform is particularly valued by enterprises in regulated industries such as healthcare, finance, and manufacturing that require secure, traceable, and compliant messaging solutions with global delivery capabilities and enterprise-grade SLAs.