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.

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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  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/Type Script 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…