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92,000+ live jobsSenior ML Engineer - Email Security
Remote, Madrid·Added 5 days ago (last checked 26 Oct)
Cloudlinux
11 open roles
Our summary
- Work mode
- Remote (Madrid)
- English
- Required
- Experience
- 5+ years
- Benefits
- Private health insurance
Visa options
The ad doesn’t mention sponsorship
Not a refusal, but not a yes. Worth asking in your first message.
Skills
Requirements
What we're looking for
- 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.
Nice to have
- 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.
Pay & benefits
What you'll get
- 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.
The role
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'll 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.
About Cloudlinux
CloudLinux is a software company that develops operating systems and security solutions for Linux-based hosting environments. Its flagship product, CloudLinux OS, is a commercial Linux distribution designed for shared hosting providers, offering enhanced security, stability, and performance through features like LVE (Lightweight Virtual Environment) and KernelCare, which provides live kernel patching without reboots. The company also offers products like Imunify360 for server security and KernelCare for enterprise systems, serving a global customer base of hosting companies and data centers.
CloudLinux has a significant presence in Spain, with a development office in Valencia, which is a key hub for its engineering teams. The company is known for its remote-first work culture, allowing employees to work from anywhere, and it actively hires international talent for roles in engineering, security, and infrastructure. For international professionals, CloudLinux offers a collaborative environment with a focus on open-source technologies and cutting-edge systems software, making it an attractive option for those seeking remote work in the tech industry.
- Founded
- 2009
- Employees
- 200–500
- Headquarters
- Palo Alto, USA
- In Spain
- Valencia
Good to know if you are moving
- CloudLinux offers fully remote positions, allowing employees to work from anywhere in the world, including Spain.
- The company has a development office in Valencia, Spain, which serves as a hub for engineering and security teams.
- CloudLinux is known for its focus on open-source technologies and contributions to the Linux ecosystem, which can be appealing for developers.
- The company provides a flexible work environment with a strong emphasis on work-life balance and professional growth.
- International hires can expect a collaborative culture with team members distributed across multiple time zones.
In their own words
About the company & team
CloudLinux is a global remote-first company. We are driven by our 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 to increase the efficiency of their operations. Every person on our team supports each other and does what we can to ensure we all are successful.
Check out our website for more information: https://cloudlinux.com/
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.
Additional information
By applying for this position, you consent to the processing of your personal data as described in our Privacy Policy (https://cloudlinux.com/candidate-privacy-notice), which provides detailed information on how we maintain and handle your data.
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