Post is used for a job or position in rather specialized contexts - military, public service, or the media. It is not common in other industries.
The soldier was punished because he left his post without permission. (A post is the place where a soldier is assigned to do his duty.) The captain posted two soldiers to guard the prisoner.
here in office the POST mean "Designation" on which designation a particular person works. Like You said inspector, inspector is not a job but inspector is a person whose post is this and his work is Inspection.
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