My dad happens to lead the e-commerce division at a logistics company and from what I've heard, Indian Post Office is not a major player at all. A large of e-commerce companies/startups are using Bluedart (now merged with DHL) as their primary logistics provider and tracking is provided as a service to the customers. Flipkart, I believe, runs their own logistics service.
Flipkart, Myntra etc run their own logistics unit Bangalore only and maybe other metros too, but when it's about tier 2 cities and blow the traditional courier firms handled it.
