Senior ML Engineer - Email Security

About CloudLinux

CloudLinux is a global remote-first company. We deliver high-volume, low-cost Linux infrastructure and security products that help companies increase the efficiency of their operations. Every person on our team supports each other to ensure collective success.

CloudLinux Inc. develops the Imunify family of security products, designed to protect hosting environments from cyber threats. Imunify Email protects hosting servers against spam, phishing, and other email-based threats across roughly 5,000 hosting servers.

Role Overview

We are replacing our current rspamd filtering system with a custom-trained transformer model that runs on the customer's CPU in under 100 MB and outperforms rspamd at every operating point.

We are looking for a Senior Machine Learning Engineer to join our team and work alongside the lead engineer responsible for our spam-filtering pipeline and ML model. Together, you will drive the development, improvement, and production rollout of our email security technology.

What You Will Do

• Model Lifecycle Management: Train, evaluate, and release spam-detection models, including corpus building, threshold selection, precision/recall analysis, and release decisions.
• Go Infrastructure: Build production services in Go, including the inference service, mail-filter integration, tokenizer, and streaming message parser.
• End-to-End Quality: Fix detection issues end-to-end (from customer report to rule/corpus fix or retraining), balancing false-positive risks against catch rates.
• Training Infrastructure: Maintain corpus tooling and training infrastructure.
• Code & Model Reviews: Review classifier, rule, and model changes to maintain high team velocity.
• Technical Support & Communication: Explain scoring logic to partner engineers and write specs, handbooks, and post-mortems for knowledge sharing.

Your First Six Months

• Month 1: Ship a rule-model release independently.
• Month 3: Merge your first piece of the new engine into staging.
• Month 6: Execute a full model release while the principal engineer is away.

Requirements

• 5+ years of experience shipping detection or classification systems where false positives carry significant operational costs (e.g., anti-spam, anti-phishing, anti-malware, fraud, abuse).
• Production ML Deployment: Track record taking at least one ML classifier to production end-to-end (corpus construction, threshold selection, error analysis).
• PyTorch & Transformers: Hands-on experience with transformer training in PyTorch (tokenizers, masked-language pre-training, fine-tuning, ONNX export, CPU inference measurement).
• Linux & Scripting: Strong proficiency in Linux, shell scripting, and Python in shared server/GPU environments.
• Modern Workflows: Daily usage of AI coding agents and development tools.
• Communication: Upper-Intermediate (B2+) or higher English proficiency, with strong written technical communication skills for specs, documentation, and PR descriptions.

Strong Pluses

• Knowledge of email internals: SMTP, MIME, transfer encodings, SPF / DKIM / DMARC, and mail filtering in Exim, Postfix, or Dovecot.
• Experience creating embedded or resource-constrained models (quantization, distillation, strict latency/memory budgets).
• Experience with Go or Rust for high-performance systems code (parsers, streaming, concurrency).
• Familiarity with rspamd or SpamAssassin internals (rules, composites, Lua plugins, mass-check scoring).
• Experience managing multi-million-sample corpora, labeling pipelines, or LLM-based annotation scaling.
• Familiarity with hosting control panels: cPanel, Plesk, DirectAdmin.

Benefits & Perks

• 100% Remote: Flexible working hours allowing you to work from any location worldwide.
• Paid Time Off: 24 days of paid vacation per year, 10 national holidays, and unlimited sick leave.
• Health & Wellness: Compensation for private medical insurance, plus reimbursement for co-working spaces and gym/sports activities.
• Growth: Dedicated education budget and continuous professional development opportunities.
• Innovation Reward: Opportunity to receive financial rewards for patentable ideas.