MSA is a highly multi-disciplinary group started in 2019 to tackle difficult mail delivery, spam, abuse, and account security problems that impact the Proton ecosystem. We built sophisticated systems from scratch that combine big data, human intelligence, machine learning, and AI agents to make tens of millions of realtime or asynchronous decisions each day. Our custom systems have reduced spam filter misclassifications by over 80% and protected millions of users from account compromise by attackers. In order to move fast with limited resources, we are organized into autonomous teams responsible for the whole system, with fullstack expertise across infrastructure, data storage, backend, frontend, machine learning, and AI agents. We are looking for humble, mission-driven, systems-thinking people who want to make a big impact in a startup environment.