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# ML Engineer

- **Company:** Cloudlinux Inc.
- **Location:** Madrid, Spain (Remote available)
- **Contract:** Permanent contract
- **Skills:** Bash Shell, Code Review, Encodings, Linux, Domainkeys Identified Mail, Domain-Based Message Authentication Reporting and Conformance (DMARC), Email Filtering, Message Transfer Agent, Internet Message Access Protocols, Python (Programming Language), Lua (Scripting Language), Machine Learning, Simple Mail Transfer Protocols, Multi-Purpose Internet Mail Extensions (MIME), Performance Tuning, Anti-Phishing, Data Streaming, Pytorch, Large Language Models, Concurrency, AI Coding Agents, Postfix, SpamAssassin, ONNX (Open Neural Network Exchange) Format, Malware Detection
- **Published:** October 24, 2026
- **Apply:** https://www.adzuna.es/details/5939601816

## About the Role

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, 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.

## Description

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 replacing it with a transformer we trained ourselves that runs on the customer's own CPU in under 100 MB and already beats rspamd at every operating point we measured. 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, 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.

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., * 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.