Internet facilities can be found in most major markets, but are often holes-in-the-wall with a handful of grimy, outdated terminals. For laptop toters, Wi-Fi hotspots have sprung up.
One centrally located post office is on the roundabout just southwest of Connaught Place; another is the Eastern Court Post Office on Janpath. Hotels usually have mailing facilities, too. DHL outlets are available around the city, but you'll pay a premium—possibly as much as your own plane ticket—to ship anything heavy to the West (just sending documents will cost you at least $60). Use Speed Post at the main post office, which is a fraction of the price and usually reliable. Be prepared to wait (and wait some more).
Main Post Office (Baba Kharak Singh Marg, at Ashoka Rd., Connaught Pl., Central Delhi, Delhi, 110001. www.indiapost.gov.in.)