Senior Software Engineer, Web Services

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 for our free products and subscriptions for upcoming cloud services, allowing us to build sustainable technology that puts users first.

To learn more, visit www.thunderbird.net

The Opportunity:

As a Senior Software Engineer, Web Services, you’ll help shape the future of email by building with leading-edge technologies such as JMAP, solving complex technical challenges, and directly influencing product direction. You’ll join the Web Services Team, which is extending Thunderbird beyond its core Desktop and Mobile products by building the systems and infrastructure that power Thunderbird, and by developing innovative web products that ensure a sustainable open-source future.

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. 

What you’ll do: 

• Lead significant technical initiatives by scoping, planning, and prioritizing features in collaboration with the team.
• Shape the product vision by advocating for user needs, influencing feature development, and contributing to long-term roadmaps.
• Drive quality and reliability through thoughtful design, testing, and code reviews. Stay up-to-date with industry trends and changes, and apply that knowledge to our product.
• Design, build and maintain services in Python and Typescript. Analyze complex email delivery issues, and optimize our configuration and infrastructure to improve our email deliverability and performance.
• Work collaboratively with global teams, including designers, engineers, and community contributors.
• Support the ongoing stability of our services alongside the team, including occasional participation in a shared on-call rotation.

What you’ll bring: 

• 7+ years of experience in software engineering, with significant hands-on experience in web infrastructure, service architecture, or DevOps, including leading large-scale or mission-critical projects.
• 2+ years of email development. This includes building, configuring and maintaining email services and infrastructure, as well as working with email deliverability and authentication concepts (e.g., DMARC/DKIM/SPF, domain warm-up, spam triggers, etc.).
• 5+ years of experience building and maintaining web services throughout the stack, from writing backend services to deploying and monitoring them in the cloud.
• 2+ years of experience with Python 3.
• Proven track record of owning features end-to-end, from gathering requirements to the delivery and maintenance of the final product.
• Great communication skills (both written and verbal), documentation skills, and the ability to work with a multi-disciplinary, geographically distributed team.
• Deep respect for the different skills and perspectives that people of varied te