Principal ML Engineer

Principal Machine Learning Engineer About Mimecast The work people build is worth protecting, and it's harder to protect than it used to be. AI agents now move at machine speed with human-level access, and a small slip-up can become a very public one. We disrupt cybercriminal activity before that happens. We think fast, go big, and always demand more of ourselves. We work hard, deliver, and repeat. We grow with real determination and put success well within reach. We push each other to be better and expect to be pushed back, in a community built on respect, where everyone is counted. Work Protected. Overview As a Principal Machine Learning Engineer, you will set technical direction for Mimecast's ML capabilities, including our GCI products or advanced email threat-detection products. This is a senior individual-contributor role: you will own the hardest modeling and systems problems end to end, define the architecture other engineers build on, and be a technical authority for product and engineering leadership when the direction is not obvious. Our threat ML runs on Mimecast's shared AI enrichment platform, the detection and extraction infrastructure serving models across the product suite. You will work at the intersection of applied ML, production model serving, and cross-team integration, making architectural decisions that hold up under production load and customer commitments. Mimecast is an AI-first engineering organization. You will use AI development tools, including Claude Code, Cursor, and MCP integrations, in your daily work and establish the workflows, patterns, and quality bar for the team. You will also design product systems using LLM and agent-based patterns. Employees are expected to work from the office at least two days per week. This fosters collaboration, communication, performance, and learning; drives innovation and creativity within and between teams; introduces employees to priorities beyond their immediate realm; and supports important interpersonal relationships and connections. What You'll Do - Develop and own ML systems end to end, from data sourcing, cleaning, and labeling strategy through feature engineering, model development, deployment, and monitoring. - Set the ML architecture across model design, serving, and surrounding systems, optimizing accuracy, latency, and throughput for highly imbalanced threat-detection data. - Set technical direction for production model serving using AWS SageMaker, NVIDIA Triton Inference Server, ensemble/KServe patterns, hardened container images, and integration with enrichment and gateway layers. - Benchmark and prototype alternatives to de-risk major decisions, then give leadership defensible technical recommendations. - Establish reproducible ML standards, including versioned datasets, region-partitioned data, and shared experimentation workflows. - Make model observability and efficacy measurement first-class concerns through distributed tracing, threshold-independent metrics, raw-payload capture, and monitoring for real regressions. - Own capacity planning and rollout strategy, including throughput per core or GPU, utilization headroom, peak-load provisioning, and phased regional canary or shadow deployments. - Diagnose production incidents, close the structural gaps they expose, and act as a primary reviewer and mentor across the ML codebase. - Partner with Product, platform engineering, and adjacent teams to shape the roadmap and communicate technical complexity and business implications through engineering and product leadership. What You'll Bring Breadth across transformer architectures, RNNs, CNNs, generalized linear models, and gradient-boosted trees, with the judgment to select the right approach for the problem rather than defaulting to the largest model. Deep Python proficiency