Senior Full-Stack Engineer, Email Systems

MZLA Technologies Corporation (MZLA) is a wholly owned, for-profit subsidiary of the Mozilla Foundation and home to Thunderbird, our flagship open-source email and productivity platform empowering more than 20 million people around the world. While part of the Mozilla portfolio of companies, MZLA operates independently in both identity and organizational structure from the Mozilla Foundation and Mozilla Corporation. Everything we build at MZLA is open source, developed transparently and in collaboration with a global community of contributors. This open approach shapes not only our products but also how we work: collaboratively, inclusively, and with a shared commitment to building technology that puts users first. We believe privacy and productivity should coexist, and that people deserve powerful digital tools without surrendering control of their data. MZLA is a small but growing team of 50+ people distributed across seven countries. As we evolve Thunderbird from a single application into a suite of privacy-respecting productivity tools, we’re introducing new products and services that remain independent of big tech ecosystems. Our unique revenue model combines community donations that keep Thunderbird freely available with subscriptions for new cloud-based services, allowing us to grow and innovate while remaining independent and true to our values. To learn more, visit www.thunderbird.net The Opportunity: As a Senior Software Engineer, Web Services, you’ll contribute to a whole new suite of communication tools including end-to-end encrypted file sharing, an email service, an appointment booking service, and more. You’ll join the Web Services Team, which is responsible for building and maintaining the accounts and email services that power these offerings. The ideal candidate will have a strong focus on web development, infrastructure, and service architecture. This person has direct experience with email delivery, is autonomous, and can lead feature development from an ambiguous project statement to a concrete plan and implementation. You are passionate about delivering quality to customers and naturally think about products from the user’s perspective, always seeking ways to improve and elevate the experience. You’ll work closely with designers, engineers, and community members to develop and maintain user-facing features and help diagnose and resolve email issues at scale. The ideal candidate has strong full-stack development experience and demonstrates collaboration, ownership, and a commitment to building reliable services. What you’ll do: Build and prototype new features and solutions to tackle complex technical challenges. Develop and maintain metrics to monitor email delivery rates and sender reputation, and diagnose service-level issues. Monitor email industry standards, trends, and emerging threats, and propose improvements to strengthen delivery, reputation, and spam resilience. Develop, test, and evolve the code architecture to ensure scalability, maintainability, and robustness. Conduct code reviews to ensure adherence to quality standards and best practices, and contribute to technical strategy and architectural decision-making. Along with our designers and product leads, build and deploy prototypes and experiments to improve workflows, conversions, and privacy-respecting analytics capabilities. Evaluate and implement systems and improvements across security, logging, performance, and accessibility. Support the stability and reliability of our services, including participation in a shared on-call rotation. What you’ll bring: 7+ years of professional software development experience, including 2+ years in a Senior Software Engineer role. 2+ years of experience with JavaScript/TypeScript and 2+ years working with Python 3. Experience building and maintaining email services. Experience building and maintaining web applications. Experience working across the full software development life cycle, from product inception through customer delivery. Deep respect for diverse skills and perspectives, with an ability to collaborate effectively across technical and non-technical teams. Ability to translate wireframes, style guides and design direction into polished, production-ready visual experiences. Proven ability to deploy and manage web infrastructure on AWS or similar cloud providers. Strong attention to detail, with excellent learning and exploration skills and a product-focused mindset that looks beyond the code to consider user needs and business goals. Excellent English written and verbal communication skills, with the ability to clearly and concisely engage with an international, geographically distributed team. Commitment to collaboration, open development, and building secure, privacy-respecting technology aligned with Thunderbird and MZLA’s values. Bonus points for: Background in Java and/or Rust development. Familiarity with Stalwart (email server). Hands-on work developing and maintaining an Identity Provider (IdP) such as Keycloak or similar. Practice writing Infrastructure as Code (IaC), ideally with Pulumi. Contributions to open-source projects or active engagement with open-source communities. Work Environment: You’ll work with passionate staff and open-source community members from all over the globe to support the mission and objectives of MZLA and Thunderbird. Strong communication and documentation skills are essential for effective collaboration. What you’ll get: 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, outlined below. Work & Career Fully remote work & schedule flexibility Latest Laptop Discretionary Annual Bonus Program Monthly Remote Work Stipend Annual Professional Development Stipend Access to Udemy Learning Platform Industry Conferences Company All Hands 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 Pension 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 also value authenticity. We want to hear your perspective, not a bot’s. It's fine to use AI to polish your writing, but not to write your answers. Candidates who submit unoriginal AI generated answers will be disqualified from further screening. MZLA Technologies Corporation (MZLA) 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. Mozilla 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.