About REX5
Meet Sebastian Sejzer.
I founded REX5 to help growing agencies make client access, recovery, and security evidence manageable in everyday operations.
The founder
Technical experience connected to your agency’s decisions.
I bring 20+ years of hands-on technical experience across infrastructure and IT. I have 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), I 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 UBS (2023–2025), I was Associate Director and Senior Cyber Security Automation Engineer, developing IBM Security SOAR integrations and incident-response automation.
Earlier, at MyHeritage (2021–2023), I worked as Senior IT Systems Administrator across corporate systems, identity, device management, automation, and documentation. My earlier work includes operational procedures at Kaltura, enterprise infrastructure at IBM and Hewlett-Packard, and running an IT outsourcing company in Argentina.
My 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 my career history, not REX5 clients.
Sebastian on LinkedIn →Working together
Clear owners. Practical changes.
I start with the owner’s business concern and the requirement behind it. Together with your IT provider and staff, I map the systems and access involved, agree priorities and change authority, then document decisions and evidence in accounts your agency 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.
See Agency Security Readiness →Start by email
Tell me what you need help with.
Tell me your company, what concerns you or what a customer is asking for, and any deadline. I’ll reply with clarifying questions and a proposed way forward. A call can follow if useful.
Email Sebastian ↗No mail app? Write to sebastian@rex5.com.