Senior Mobile Engineer, iOS

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 and productivity tools that help people manage their digital lives while staying in control of their data. We are open source by design, developing our products transparently and in collaboration with a global community of contributors. Our small but growing company of 60+ people is distributed across seven countries, and we’re expanding across desktop, mobile, paid services, and new product experiences.

MZLA Technologies Corporation is the nonprofit-owned company behind Thunderbird and part of the Mozilla family, with its own compensation programs, benefits, and employment policies.

About the role

As a Senior Software Engineer, iOS, you’ll bring deep iOS expertise to the design, development, and evolution of Thunderbird’s iOS application. You’ll work closely with mobile engineers, product management, UX, and other partners to deliver a high-quality iOS experience that meets high standards for performance, reliability, accessibility, security, and maintainability. You’ll play an important role in delivering exceptional user experiences for Thunderbird’s global user base by translating product needs into thoughtful technical solutions and ensuring your work aligns with MZLA’s mission.

Responsibilities

• Build and refine Thunderbird’s mobile products and platform architecture.
• Improve scalability, performance, reliability, and user experience.
• Develop a deep understanding of the codebase and architecture to confidently make changes across the entire stack.
• Maintain strong debugging and testing practices across unit, integration, and automated testing.
• Review code and guide improvements to architecture, testing, and development best practices.
• Independently resolve complex issues involving performance, security, and cross-platform integration.
• Monitor application health and address issues before they escalate.
• Document technical decisions, system architecture, and team processes.
• Own assigned projects, collaborating cross-functionally from investigation and planning through development, validation, and delivery.
• Ensure mobile development meets accessibility, security, and privacy standards.

Requirements

• 7+ years of professional software development experience, including 2+ years in a Senior Software Engineer role.
• 3+ years of professional mobile application development experience.
• Strong experience with Swift, SwiftUI, and iOS frameworks.
• Deep knowledge of iOS architecture, design patterns, and performance optimization.
• Experience delivering and maintaining complex, scalable, and reliable software.
• Experience addressing technical debt and refactoring large or complex codebases.
• Strong knowledge of mobile security, including encryption, secure storage, app signing, and vulnerability remediation.
• Experience with communication and email protocols such as RSS, IMAP, POP, or Matrix, and familiarity with IETF standards for CalDav or CardDav.
• Advanced proficiency with Git and collaborative development workflows.
• Strong debugging, testing, and problem-solving skills.
• Strong attention to detail, curiosity, and a product-focused mindset.
• Ability to work independently, take ownership, and collaborate across teams.
• Respect for diverse skills, experiences, and perspectives.
• Excellent async written communication skills; comfortable working with a geographically distributed team.
• Ability to learn, evaluate, and responsibly use emerging technologies, including AI-enabled tools, to improve work processes.

Nice to have

• Familiarity with Apple App Store and Google Play Store compliance guidelines.
• Experience contributing to open-source projects or communities.
• Proficiency in French, German, Japanese, or another widely supported Thunderbird language.

What success looks like

You’ll be successful in this role if you look beyond shipping features and improve the architecture, reliability, security, and long-term health of the product. You’re comfortable solving ambiguous problems, flagging risks early, documenting decisions, and collaborating across engineering, product, UX, users, and the open-source community. Over time, your work will help Thunderbird’s iOS experience become more resilient, scalable, and easier for both staff and community contributors to build on.

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.

Pay

We benchmark our base salaries to local markets and target the 60th percentile of the peer market. The salary range for this role in the US is $123,000 - $144,000 USD. Title, level, and compensation will be determined based on qualifications and experience.

Benefits

• Work & career
  • Fully remote work & schedule flexibility
  • Company-provided laptop
  • Annual bonus program
  • Monthly remote work stipend
  • Annual professional development stipend
  • Access to Coursera learning platform
  • Industry conferences
  • Company all-hands and team gatherings
• Rest & play
  • 24 days PTO per year (prorated)
  • Your birthday off
  • Year-end company shutdown
  • 9 wellbeing days
  • Public holidays
  • Other paid leave
  • Quarterly wellbeing stipend for personal/family activities
• Health & family
  • 401(k) contributions
  • Health, dental, & vision insurance
  • Disability insurance
  • Life insurance
  • Employee assistance program
  • Paid parental leave
  • Paid sick days