ML engineer in email security

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 we train in-house. We are looking for a Senior Machine Learning Engineer to join our team

• Train, evaluate, and release spam-detection models: build the corpus, pick the threshold, read the precision/recall report, decide ship or retrain
• Build the production side of the new engine in Go: the inference service, the mail-filter integration, the tokenizer, the streaming message parser
• Fix detection quality end to end, from a customer's "this phishing got through" to a rule, a corpus fix, or a retrain, with the false-positive cost weighed against the catch
• 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. That is how this team transfers knowledge

• 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, abuse
• You have taken at least one ML classifier to production yourself: corpus construction, threshold selection, error analysis
• Hands-on transformer training in PyTorch: tokenizers, masked-language pre-training, fine-tuning, ONNX export, 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
• Будет плюсом: Email internals: SMTP, MIME, transfer encodings, SPF / DKIM / DMARC, how Exim, Postfix, and Dovecot handle mail to a filter; Experience in creating embedded models; Go or Rustfor systems code: parsers, streaming, memory budgets, concurrency; rspamd or SpamAssassin internals: rules, composites, Lua plugins, mass-check scoring; Multi-million-sample corpora, labelling pipelines, annotator tooling; Small models for constrained hardware: quantization, distillation, latency budgets; LLM-based labelers or validators for scaling annotation; Hosting panels: cPanel, Plesk, DirectAdmin

• A focus on professional development
• Interesting and challenging projects
• Fully remote work with flexible working hours, that allows 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 leaves
• 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