Use ～を通して when specifying the medium, intermediary, or experience by which something is accomplished — routing a negotiation through an agent, learning something via a project, or covering a whole span of time (一年を通して). It is standard in written reports, email, and formal speech; the near-synonym ～を通じて is slightly more written/formal and favors abstract channels, while ～を通して leans toward active, deliberate use of a means. For simple physical routes or instruments, plain ～で or ～経由で is more natural.