Senior Machine Learning Engineer, Email Security at CloudLinux

About CloudLinux

CloudLinux is a global remote first company driven by a set of core principles: do the right thing, employees first, we are remote first, and we deliver high volume, low cost Linux infrastructure and security products that help companies increase the efficiency of their operations. Every team member supports each other and works to ensure collective success.

CloudLinux Inc. develops the Imunify family of security products, designed to protect hosting environments from a wide range of cyber threats. One of these solutions is Imunify Email, an email security product that protects hosting servers against spam, phishing, and other email based threats.

Imunify Email filters mail on about 5,000 hosting servers. Today the filter is rspamd with rules and a scoring model trained in house. The team is replacing it with a transformer they trained themselves that runs on the customer's own CPU in under 100 MB and already beats rspamd at every operating point measured.

The Role

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

What You Will Do

• Train, evaluate, and release spam detection models: build the corpus, pick the threshold, read the precision/recall report, and decide whether to ship or retrain.
• Build the production side of the new engine in Go: the inference service, the mail filter integration, the tokenizer, and the streaming message parser.
• Fix detection quality end to end, from a customer's "this phishing got through" report to a rule, a corpus fix, or a retrain, weighing the false positive cost against the catch rate.
• Keep the corpus tooling and training infrastructure running.
• Review and approve classifier, rule, and model changes so no release waits on one person.
• Answer partner engineers who ask why a message scored the way it did.
• Write specs, handbooks, and post mortems, which is how this team transfers knowledge.

Your First Six Months

• Month 1: you ship a rule model release on your own.
• Month 3: your first piece of the new engine is merged and running on staging.
• Month 6: a model release goes out while the principal engineer is away.

Requirements

What You Bring

• 5+ years of shipping detection or classification systems where false positives have a cost you had to defend: anti spam, anti phishing, anti malware, fraud, or abuse.
• You have taken at least one ML classifier to production yourself: corpus construction, threshold selection, and error analysis.
• Hands on transformer training in PyTorch: tokenizers, masked language pre training, fine tuning, ONNX export, and CPU inference measurement.
• Linux, shell, and Python on shared servers and a shared GPU.
• Daily usage of AI coding agents and tools.
• English at upper intermediate (B2) level or higher, with particularly strong written communication skills for technical documentation, specifications, and code reviews. Your specs and merge request descriptions count as much as your code.

Strong Plus If You Have

• Email internals: SMTP, MIME, transfer encodings, SPF / DKIM / DMARC, and how Exim, Postfix, and Dovecot handle mail to a filter.
• Experience in creating embedded models.
• Go or Rust for systems code: parsers, streaming, memory budgets, and concurrency.
• rspamd or SpamAssassin internals: rules, composites, Lua plugins, and mass check scoring.
• Multi million sample corpora, labelling pipelines, and annotator tooling.
• Small models for constrained hardware: quantization, distillation, and latency budgets.
• LLM based labelers or validators for scaling annotation.
• Hosting panels: cPanel, Plesk, DirectAdmin.

Benefits

• A focus on professional development.
• Interesting and challenging projects.
• Fully remote work with flexible working hours, allowing you to schedule your day and work from any location worldwide.
• Paid 24 days of vacation per year, 10 days of national holidays, and unlimited sick leave.
• Compensation for private medical insurance.
• Co working and gym/sports reimbursement.
• Budget for education.
• The opportunity to receive a reward for the most innovative idea that the company can patent.

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