Senior Backend Engineer (.NET / C#)

Join us as a Senior Software Engineer on the platform team behind the PostNL mobile app. We build a server-driven UI backend in C# and .NET 9: the server decides what every screen looks like, so we ship UI changes without waiting for an app release. You bring deep C# expertise, care about clean architecture, and want your work to land in the hands of millions of users the moment you deploy.

Why you choose PostNL as a Senior Backend developer

Leverage: Our platform powers the entire PostNL mobile app. Every screen the app renders is described by us. When you ship a change, it reaches every user on Android and iOS without an app store release, sometimes within minutes. Few backend roles have this kind of immediate reach.

Architecture that matters: Server-driven UI is not a buzzword for us, it is the design that lets a small platform team move the whole app forward. You will work on the screen handlers, section builders, and contracts that mobile teams build on top of. The decisions you make about those abstractions shape what the app can do for years.

Great Atmosphere: You join a team that collaborates across disciplines and takes quality seriously. Decisions are made by the people doing the work, and ideas are judged on their merits rather than on who brought them.

Freedom: You combine working from home with two days per week at our office in the historic Stationspostgebouw, right next to Hollands Spoor station. You have a real say in how the team works and where the platform goes.

Growth: As a senior you mentor others, set technical direction, and keep growing yourself through training, tech communities, and exposure to different parts of PostNL's engineering organisation.

Your role

In this role, you make sure our mobile app shows the right information in the right way. You design how complete screens are built and delivered to the app. Instead of sending separate pieces of data, you decide what a user sees, in what order, and what happens when they take action. This means you think from the user’s point of view and turn that into clear, logical solutions that work smoothly in the app.

You work closely with colleagues, such as the mobile team, to agree on how everything connects. You take ownership of the quality of what we build and look for ways to improve it every day. As a senior, you guide others, share your knowledge, and help the team grow. You also play an important role in shaping how we work and making sure we keep delivering a reliable and user-friendly experience.

Your team

You join the Server-Driven UI Platform team, a cross-functional team of engineers, UX designers, analysts, a solution consultant, and a product manager. The team owns the platform end to end, from contracts with the mobile teams through production operation. You will work alongside the engineers already on the team and help lead its next phase.

What we deliver you

A role full of innovation and work that you will see reflected across the Netherlands. At PostNL, your mindset meets our challenge. You can count on an attractive package of employment conditions. The top benefits for your role include:

• Salary between €4,558 and €7,550 gross per month based on 37 hours per week. Working 32 hours is also possible!
• Hybrid working and flexible hours. Work two or more days from home? Receive €45 net per month.
• 8% holiday allowance and 25 vacation days for full-time work.
• Travel allowance for commuting: NS Business Card or kilometre reimbursement.
• A solid pension scheme via the PostNL pension fund.
• Engineering Laptop (Mac or Windows) and smartphone.
• Training and development opportunities via the PostNL Academy.
• Discounts on holidays, events and products.

What you bring

You are a senior engineer who takes ownership of more than your own code. You think about the team's technical direction, you mentor others, and you care about the platform's users (other engineers and the mobile teams) as much as the stack. You communicate clearly about trade-offs and you enjoy working with designers, analysts, and product people.

You also bring the following:

• Around 8 years of experience building backend systems at scale, with a track record of shipping production services to many users.
• Strong C# and .NET expertise. We are on .NET 9.
• Solid grasp of Clean Architecture and layered architecture patterns, and the judgment to know when to bend them.
• Hands-on experience with CQRS, ideally with MediatR.
• Comfortable working with AWS, in particular DynamoDB, Lambda, SNS, and SQS.
• Experience setting technical direction on a team: reviewing designs, raising the quality bar, and mentoring others.

Nice to have, not required:

• Experience with server-driven UI patterns from either side (backend or mobile).
• Familiarity with mobile app integration (Android, iOS, or both).