For buyers contracting authority
Choose 72611000 when the contract keeps existing IT running rather than building something new: server and network support, helpdesk and incident handling, system administration, and the engineer hours that wrap around a live estate. A contracting authority reaches for it for managed-service deals and technical support frameworks that recur on fixed cycles.
The boundary that trips authorities is the software layer. Support and maintenance scoped to a specific application belongs to Software support services (72261000); 72611000 is the broader technical support of the computing environment itself. Where a contract spans servers, networks and end-user devices, this code fits better than a software-specific one.
One more line to watch: hardware. Repairing and maintaining the physical equipment is Maintenance and repair of computer equipment (50312000). Keep a bundled deal here when technical support of the running environment is the main purpose, and tag the primary CPV code by whichever scope dominates the statement of work.