GreenArrow is an enterprise-grade high-volume email delivery platform and Mail Transfer Agent (MTA) developed by DRH Internet Inc. Since its inception in 2003, the software has focused on providing high-scale senders, such as Email Service Providers (ESPs) and large-scale marketers, with granular control over their delivery infrastructure. The platform is available as either self-hosted software for Linux environments or as a fully managed cloud service.

The core of the system is the GreenArrow Engine, a high-performance MTA designed to process millions of messages per hour. It supports multiple injection methods, including SMTP, HTTP API, and local pipes. Its architecture is built for reliability and speed, utilizing a sophisticated multi-queue system to manage high-throughput delivery while maintaining system stability.

Technically, GreenArrow is defined by its deliverability management tools. It features "VirtualMTAs," which allow administrators to segment traffic across specific IP pools to protect sender reputation. Its "Dynamic Delivery" engine automatically adjusts connection limits and sending rates based on real-time feedback and deferral codes from ISPs. Additionally, the platform provides automated bounce processing, Feedback Loop (FBL) integration, and native support for DKIM, SPF, and DMARC.

For users requiring more than raw delivery, the GreenArrow Marketing Studio provides a campaign management layer with list segmentation, automated triggers, and a drag-and-drop editor. The platform also offers "GreenArrow Monitor" for seed-list testing and inbox placement analytics. These modular components allow organizations to use GreenArrow as a specialized delivery engine or as a comprehensive, end-to-end email marketing solution.