Office.js Developer

Oscar Associates Ltd

Senior Outlook Add-In Developer (Office.js) | Hybrid | London/Sheffield | 10 Month Contract | £500 – £550 inside IR35

About the Role

We’re looking for a seasoned Senior Outlook Add-in Developer to join our team and take ownership of designing, building, and supporting sophisticated Outlook add-ins used in large, enterprise-scale environments.

This role is ideal for someone who thrives in complex messaging ecosystems and has hands-on experience delivering solutions that work flawlessly across Windows, macOS, web, and mobile Outlook clients, including hybrid Exchange setups spanning on-premises and Microsoft 365.

What You’ll Be Doing

• Architect, develop, and support Outlook add-ins using Office.js and modern web technologies

• Ensure add-ins perform consistently across Outlook for Windows, Mac, Web, and Mobile

• Integrate Outlook add-ins with Back End services, APIs, and identity platforms such as Microsoft Graph and Azure

• Focus on performance, security, and reliability in high-volume email scenarios

• Diagnose and resolve issues across multiple Outlook clients and platforms

Core Technical Experience

• Demonstrated experience building Outlook add-ins in enterprise environments

• Strong skills in Office.js, JavaScript/TypeScript, HTML, and CSS

• Hands-on experience with hybrid Exchange (on-prem + Exchange Online)

• Solid understanding of Microsoft 365, Outlook desktop clients, and Outlook Web App behavior

Nice to Have

• Experience with Azure services (App Services, Functions, Storage, Key Vault)

If this sounds like you, APPLY NOW!

Senior Outlook Add-In Developer (Office.js) | Hybrid | London/Sheffield | 10 Month Contract | £500 – £550 inside IR35

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