How we built a load testing framework for email security at scale

Sublime has developed Mjölnir, a specialized load testing framework designed to meet the unique demands of email security platforms and simulate enterprise-scale traffic. Existing tools like k6, Gatling, and JMeter were insufficient for emulating realistic email behaviors and handling Google Workspace or Microsoft 365 API simulations, prompting the creation of Mjölnir. This framework employs a producer/consumer architecture to separate email preparation from sending, ensuring precise timing and efficient memory use. Mjölnir's realistic email address generator and suffix-compressed radix trees manage millions of addresses efficiently, while its worker pool with configurable delay and jitter can simulate realistic, bursty email traffic patterns. The tool has effectively validated Sublime's platform capabilities, supporting inline processing and user reports under high load, and continues to evolve with additional features like API mockups for Google Workspace and Microsoft 365. Through Mjölnir, Sublime can confidently ensure their infrastructure is ready for large enterprise customers, addressing specific challenges that generic load testing tools cannot.