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

Stellenbeschreibung:

Join to apply for the Staff Software Engineer (f/m/d) C / C++ role at IONOS Group

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.

Responsibilities

Mail‑Backend Engineering
Design, develop, and scale the next‑generation MTA, IMAP, POP3, and SIEVE servers that handle 30M+ 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 30M+ 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