Senior Outlook Developer

We are seeking an experienced Outlook Add-in Developer to design, build, and support sophisticated Outlook add-ins within large-scale, hybrid enterprise messaging environments. The successful candidate will have proven experience delivering robust solutions that operate seamlessly across Windows, macOS, web, and mobile Outlook clients, and across both on-premises Exchange and Microsoft 365 Exchange Online. This role operates within a highly regulated financial services environment and requires close collaboration with cross-functional teams in an Agile delivery model to ensure solutions meet high standards for security, scalability, reliability, and performance. The role is INSIDE of IR35 and £550 P/D Key Responsibilities • Design, develop, enhance, and support Outlook add-ins using Office.js and related Microsoft technologies • Deliver consistent functionality across Outlook for Windows, macOS, Web, and Mobile • Build and support add-ins for complex, enterprise-scale email environments, including hybrid Exchange deployments and Outlook Web App (browser-based clients) • Integrate Outlook add-ins with backend services, APIs, and identity platforms such as Microsoft Graph and Azure Active Directory • Ensure full compatibility with both Exchange on-premises and Exchange Online (Microsoft 365) • Optimise solution performance, resilience, and security in high-volume email environments • Collaborate closely with product owners, solution architects, QA, and operations teams within an Agile/Scrum framework • Actively participate in sprint planning, backlog refinement, code reviews, and retrospectives • Troubleshoot, diagnose, and resolve issues across multiple Outlook clients and platforms • Contribute to technical documentation, solution designs, coding standards, and best practices Required Skills & Experience Technical Experience • Demonstrated experience developing Outlook add-ins within enterprise environments • Strong proficiency in Office.js, JavaScript/TypeScript, HTML, and CSS • Hands-on experience supporting hybrid Exchange environments (on-premises and Exchange Online) • Solid understanding of Microsoft 365, Exchange Online, Outlook desktop clients, and Outlook Web App behaviour and limitations • Experience delivering solutions across Windows, macOS, Web, and Mobile Outlook clients • Familiarity with Microsoft Graph, RESTful APIs, and authentication using OAuth / Azure AD • Experience implementing telemetry, logging, and monitoring for Outlook add-ins • Understanding of deployment, governance, and administrative considerations for Outlook add-ins within Microsoft 365 Methodology & Collaboration • Proven experience working in Agile delivery environments (Scrum or Kanban) • Strong collaboration skills, with the ability to work effectively across distributed and cross-functional teams • Ability to translate complex business and regulatory requirements into scalable, maintainable technical solutions Preferred / Nice-to-Have • Experience with Azure services, including App Services, Functions, Storage, and Key Vault • Knowledge of email security, compliance, and data governance, particularly within regulated enterprise or financial services environments • Experience with CI/CD pipelines, version control systems (e.g. Git), and automated testing frameworks