Location
Central London (Fully Remote)

Hours
Full Time

Salary
£62,000 - £72,000 GBP

About the Role
Thunderbird is one of the world’s most trusted open-source email applications, empowering more than 20 million people globally. At MZLA, the team behind Thunderbird, we build privacy-respecting communication tools that help people manage their digital lives while staying in control of their data. We are open source by design, developing products transparently and collaboratively with a global community of contributors. Our small but growing distributed team includes 65+ people across seven countries, expanding Thunderbird beyond desktop to mobile and paid services as privacy-respecting alternatives to big tech ecosystems.

The Senior Site Reliability Engineer establishes and maintains the infrastructure and operational systems that Thunderbird users and teams depend on every day. You will design and develop CI/CD systems for MZLA websites, services, and release workflows, diagnose and debug production incidents, and implement improvements to enhance system reliability. This role requires treating production as something to be understood, not just kept running, with strong documentation, proactive problem identification, and security baked into your work.

You will work closely with Software Development Engineers, team members, and community contributors, reporting to the Sr Manager, Platform Infrastructure. This is a great opportunity for someone who thrives with ambiguity, makes good decisions without a complete picture, and cares deeply about Thunderbird’s mission of open-source software used by millions who choose privacy and ownership over convenience.

This is a full-time, fully remote position with consistent overlap required with Pacific Time zone working hours for effective collaboration. We rely on clear communication, thoughtful documentation, and collaborative decision-making to work effectively across time zones and disciplines.

Compensation & Benefits
We benchmark our base salaries to local markets targeting the 60th percentile of the peer market. In addition to competitive salaries, we offer a comprehensive benefits package including fully remote work and schedule flexibility, company-provided laptop, annual bonus program, monthly remote work stipend, professional development stipend, industry conferences, company gatherings, 24 days PTO plus birthday and wellbeing days, health, dental, vision insurance, disability and life insurance, employee assistance program, paid parental leave, and more.

Experience
- 7+ years in infrastructure, platform engineering, or site reliability roles
- Hands-on production Kubernetes experience including workload operations, troubleshooting, and cluster management
- Experience with infrastructure-as-code on AWS using Terraform, OpenTofu, or Pulumi
- Security awareness in infrastructure practices including identity, least privilege, secrets hygiene, and network controls
- Proven ownership mindset with proactive issue identification and risk communication
- Excellent asynchronous written communication skills
- Ability to collaborate effectively with software engineers and non-engineering stakeholders
- Ability to learn and responsibly use emerging technologies, including AI-enabled tools

About you
- Treat production as something to be understood, not just kept running
- Write clear documentation and flag problems before they escalate
- Bring strong production instincts and experience with incident response and post-mortems
- Think in code rather than consoles, with security baked in
- Comfortable with ambiguity and making decisions without a complete picture
- Passionate about open-source software and privacy-focused technology

Qualifications
No formal qualifications required; emphasis is on experience, skills, and mindset.

Bonus Points
- Experience with GitOps workflows (ArgoCD or Flux)
- Familiarity with Keycloak or similar identity platforms (OIDC, SAML, federation)
- Knowledge of email protocols and/or experience operating email infrastructure (SMTP, IMAP)
- Prior work in or alongside an open-source community
- Proficiency in French, German, Japanese, or other languages in addition to English