Staff Software Engineer (f/m/d) C / C++

With over 4 million domains and more than 2 million customers, we, as an IONOS company, are among the largest web hosting providers worldwide. We operate two TÜV-certified data centers with over 70,000 servers. Our products are diverse and form the backbone of our success, but they only come to life through our amazing employees.

Join the Team that Powers the Future of Email – 30 Million Mailboxes & Counting!

We’re optimizing and maintaining the beating heart of IONOS’ shared‑mail platform – a mission‑critical, high‑performance stack that keeps millions of people and businesses connected every single day. If you love low‑level code, love solving “impossible” problems, and want to see your work touch 30 million inboxes, this is the place for you.

Who We Are

The Core – We own, develop, and operate the proprietary and open‑source software that runs the mail systems behind IONOS/Strato hosting packages.

Full‑Control Mindset – By keeping the code in‑house we can diagnose, fix, and ship changes at lightning speed – no waiting on third‑party tickets.

Data‑Driven Optimisation – Real‑time monitoring of the live environment fuels our continuous‑performance‑tuning loop.

Global Collaboration – You’ll work side‑by‑side with counterpart teams across Europe, sharing knowledge and shaping the roadmap together.

In short: our platform is the future of shared email, and you’ll be key to its evolution.

Tasks

• Mail‑Backend Engineering
• Design, develop, and scale the next‑gen MTA, IMAP, POP3, and SIEVE servers that handle 30 M+ mailboxes.
• Modernisation & Refactoring
• Clean up legacy code, introduce clean‑architecture patterns, and make the stack more testable and resilient.
• High‑Performance Infra
• Build rock‑solid, low‑latency pipelines, automated provisioning, and security‑first services that run 24/7.
• Tooling & Automation
• Create internal dev‑ops tools, dashboards, and alerting systems that keep the platform healthy and our engineers happy.
• Cross‑Team Collaboration
• Partner with product, security, SRE, and international engineering squads to ship features end‑to‑end.

Qualifications

• Deep Go, Rust, or C/C++ experience
• Strong grasp of SMTP, IMAP, POP3, SIEVE protocols & mail‑system internals
• Proven track record in high‑throughput, low‑latency services (10k+ req/s)
• Ability to read, understand, and improve large, existing codebases
• Familiarity with observability stacks (Prometheus, Grafana)
• Passion for test‑driven development, CI/CD, and automation
• Fluent German and English (both spoken & written)

Languages: Fluent written and spoken German and English

What’s in It for You:

Impact at Scale – Your code will run on a platform serving 30 M+ email accounts worldwide.

Autonomy & Ownership – Full control over the stack, from design to production.

International Exposure – Regular syncs with teams in the UK, Spain, Germany, Austria, Poland.

Continuous Learning – Budget for conferences, certifications, and internal tech talks.

Competitive Package – Attractive salary, performance bonus, 30 days vacation + 2 flexible remote‑work days per week.

Where You’ll Be:

Location: Berlin (HQ) – hybrid model (3 days onsite, 2 days remote).

Team Size: 5 passionate engineers; we’re expanding!

Benefits

• Hybrid working model.
• Sustainable work location in Friedrichshain.
• Permanent employment contract.
• 30 days vacation.
• Discount on gyms (Fitness First, SuperFit, FitX).
• Employee discount on STRATO products and 1&1 products.
• Bicycle leasing with Eurorad.
• Health promotion offers such as group accident insurance, flu vaccinations, eye check-ups and co-payment for workplace glasses.

Ready to Shape the Future of Email?
Apply us now!

We value diversity and welcome all applications - regardless of, for example, gender, nationality, ethnic or social origin, religion, disability, age as well as sexual orientation and identity, physical characteristics, marital status or any other irrelevant factor subject to applicable law.