Senior Site Reliability Engineer

Why Thunderbird?

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. Our products are developed transparently and in collaboration with a global community of contributors, and that same spirit shapes how we work: collaboratively, inclusively, and with a shared commitment to putting users first.

Our small but growing distributed team includes 65+ people across seven countries. As Thunderbird evolves beyond a single desktop application, we are expanding across desktop, mobile, and paid services to build independent, privacy-respecting alternatives to big tech ecosystems.

Our revenue model combines user donations, which help keep Thunderbird’s apps freely available, with paid services that cover the costs of hosted offerings while supporting long-term sustainability and continued innovation.

A note about MZLA and Mozilla: MZLA Technologies Corporation is the nonprofit-owned company behind Thunderbird and part of the Mozilla family. MZLA is separate from Mozilla Corporation and has its own compensation programs, benefits, and employment policies.

To learn more, visit www.thunderbird.net

The opportunity

The Senior Site Reliability Engineer establishes and maintains the infrastructure and operational systems that Thunderbird users and teams depend on every day. You’ll 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. We believe that good infrastructure work is invisible when it’s going well and invaluable when it isn’t.

This role is for someone who treats production as something to be understood, not just kept running. You write things down, flag problems before they become fires, and leave documentation better than you found it. You bring production instincts, infrastructure-as-code fluency, and security awareness that’s baked in, not bolted on.

You’ll 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 about Thunderbird’s mission: open-source software used by millions who choose privacy and ownership over convenience.

This role requires consistent overlap with Pacific Time zone working hours to enable effective collaboration. You should have availability for regular overlap hours for context sharing with Pacific Time colleagues.

What you’ll do

• Operate and evolve our EKS-based Kubernetes platform, supporting service migrations, platform improvements, and reliability initiatives.
• Design and develop CI/CD systems supporting websites, services, and Thunderbird desktop releases, contributing to pipeline reliability and OIDC-based authentication across GitHub Actions workflows.
• Write and maintain infrastructure in Pulumi and/or Terraform/OpenTofu across multiple AWS accounts.
• Operate and evolve our observability stack (VictoriaMetrics, VictoriaLogs, Grafana, Vector) and partner with engineering teams to incorporate instrumentation and monitoring into service design.
• Apply security-conscious infrastructure practices, including least-privilege IAM, secrets management via AWS Secrets Manager and External Secrets Operator, and network segmentation.
• Diagnose and debug production incidents; drive root-cause analysis and post-incident improvements to prevent recurring problems.
• Participate in on-call rotation and collaborate with SDEs and fellow SREs to ship, maintain, and monitor new builds and support service onboarding.
• Contribute to runbooks, architecture documentation, and team processes.

What you bring

• 7+ years of experience in infrastructure, platform engineering, or site reliability roles, including hands-on production Kubernetes experience in workload operations, troubleshooting, and cluster management.
• Hands-on experience with infrastructure-as-code on AWS using Terraform, OpenTofu, or Pulumi.
• Security awareness in day-to-day infrastructure work: identity, least privilege, secrets hygiene, and network controls.
• Demonstrated ownership mindset with the ability to proactively identify issues, drive work to completion, and communicate risks early.
• Excellent async written communication skills; comfortable working with a geographically distributed team.
• Ability to collaborate effectively with software engineers and non-engineering stakeholders to improve platform reliability and operational efficiency.
• Ability to learn, evaluate, and responsibly use emerging technologies, including AI-enabled tools, to improve work processes.

Bonus points for

• 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.
• French, German, Japanese, or other language proficiency in addition to English.

What success looks like

You’ll be successful in this role if you treat production as something to be understood, not just kept running. You write things down, flag problems before they become fires, and leave documentation better than you found it.

You bring production instincts. You’ve been paged at 2am, you know what good alerting looks like, and you’ve done the post-mortem work to make sure it doesn’t happen the same way twice. You think in code, not in consoles. Your security awareness is baked in, not bolted on. You default to least privilege and ask “what’s the blast radius?” before you ship.

You’re comfortable with ambiguity. We’re a small team building toward something, and you can make good decisions without a complete picture. Thunderbird is open-source software used by millions who choose privacy and ownership over convenience. That matters to you.

Work environment

This is a full-time, fully remote position. You’ll join a distributed team of Thunderbird staff, open-source community members, and contributors from around the world.

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 and target the 60th percentile of the peer market. The salary ranges for this role are:

• UK: £62,000 - £72,000 GBP

We may consider candidates with strong skills but less than the required experience. Title, level and compensation will be determined based on qualifications and experience.

In addition to competitive salaries, we offer a comprehensive benefits package designed to support your whole self.

Work & career

• Fully remote work & schedule flexibility
• Company-provided laptop
• Annual bonus program
• Monthly remote work stipend
• Annual professional development stipend
• Industry conferences
• Company all-hands and team gatherings

Rest & play

• 24 days PTO per year (prorated)
• Your birthday
• Year-end company shutdown
• 9 wellbeing days
• Public holidays
• Other paid leave
• Quarterly wellbeing stipend for personal / family activities

Health & family

• RRSP contributions
• Health, dental, & vision insurance
• Disability insurance
• Life insurance
• Employee assistance program
• Paid parental leave
• Paid sick days

Work eligibility

Applicants must reside in and have permanent work authorization for the country location(s) specified in the posting. We are unable to consider applicants outside of these markets at this time. And, we do not provide visa sponsorship.

How to apply

Please apply directly through our career page. We carefully review every cover letter and screening question, so take the time to answer each fully.We value authentic, thoughtful responses that reflect your own experience and perspective. It is fine to use AI tools to polish your writing, but your answers should be your own. Candidates who submit generic or unoriginal AI-generated responses may be disqualified from further consideration.

Our commitment to diversity, equity, and inclusion

MZLA believes in the value of diverse creative practices and forms of knowledge, and knows diversity, equity and inclusion are crucial to and enrich the company’s core mission. We encourage applications from everyone, including members of all equity-seeking communities, such as (but not limited to) women, racialized and Indigenous persons, persons with disabilities, persons of all sexual orientations, gender identities and expressions.

We are an equal opportunity employer. We do not discriminate on the basis of race (including hairstyle and texture), religion (including religious grooming and dress practices), gender, gender identity, gender expression, color, national origin, pregnancy, ancestry, domestic partner status, disability, sexual orientation, age, genetic predisposition, medical condition, marital status, citizenship status, military or veteran status, or any other basis covered by applicable laws. MZLA will not tolerate discrimination or harassment based on any of these characteristics or any other unlawful behavior, conduct, or purpose.

We will ensure that qualified individuals with disabilities are provided reasonable accommodations to participate in the job application or interview process, to perform essential job functions, and to receive other benefits and privileges of employment, as appropriate. Please contact us at hiringaccommodations@thunderbird.net to request accommodation.

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