About REX5
Meet Sebastian Sejzer.
Sebastian Sejzer founded REX5. REX5 provides part-time IT administration for small businesses with distributed employees and freelancers, covering onboarding, offboarding, SaaS access, and security without the cost of hiring a full-time IT employee.
The founder
IT experience for your business.
Sebastian brings 30+ years of hands-on technical experience across infrastructure and IT. He has led a distributed IT and DevOps team, built security automations, and operated the identity, devices, and systems teams depend on.
At Magma Devs (2025–2026), he was IT Manager and Infra Team Lead, coordinating a distributed IT and DevOps team across US and EU time zones and implementing JumpCloud SSO, CrowdStrike EDR, and monitoring. At the world’s largest private bank and global wealth manager (2023–2025), he was Associate Director and Senior Cyber Security Automation Engineer, developing IBM Security SOAR integrations and incident-response automation.
Earlier, at MyHeritage (2021–2023), he worked as Senior IT Systems Administrator across corporate systems, identity, device management, automation, and documentation. His earlier work includes operational procedures at Kaltura, enterprise infrastructure at IBM and Hewlett-Packard, and running an IT outsourcing company in Argentina.
His technical delivery has supported SOC 2 and ISO 27001 readiness. REX5 does not issue certifications or guarantee an audit outcome. These employers are part of his career history, not REX5 clients.
Sebastian on LinkedIn →Working together
Clear owners. Practical changes.
REX5 starts with the owner’s business concern and the requirement behind it. Together with your IT provider and staff, REX5 maps the systems and access involved, agrees priorities and change authority, then documents decisions and evidence in accounts your business controls.
The aim is a handover your team can use: what changed, who owns each remaining action, and what can be shown to a customer without overstating the controls.
Explore part-time IT administration →Start by email
Tell REX5 what you need help with.
Tell REX5 your company, what concerns you or what a customer is asking for, and any deadline. REX5 will reply with clarifying questions and a proposed way forward. A call can follow if useful.
Contact REX5 →You can also write to sebastian@rex5.com.