In the urban sprawl of Mumbai (formerly Bombay), where going to work means leaving home as early as 7 a.m., long before the woman of the house has started cooking for the day, the dabbawalla system has withstood the onslaught of office cafeterias, neighborhood eateries, multinational food chains and high-end restaurants, where table reservations are hard to come by. The dabbawallas even deliver in the pouring rain or during political strife. And business is still growing, at a steady rate of 5 percent to 10 percent a year.

The service is at once simple and complex. A network of wallas picks up the boxes from customers’ homes or from people who cook lunches to order, then delivers the meals to a local railway station. The boxes are hand-sorted for delivery to different stations in central Mumbai, and then re-sorted and carried to their destinations. After lunch, the service reverses, and the empty boxes are delivered back home.

Image A dabbawalla navigating traffic in Mumbai. Relatively small networks have begun in places like San Francisco and New York. Credit... Fawzan Husain for The New York Times

The secret of the system is in the colored codes painted on the side of the boxes, which tell the dabbawallas where the food comes from and which railway stations it must pass through on its way to a specific office in a specific building in downtown Mumbai.

“We don’t know how we could survive without this system,” said Vrinda Chiplunkar, who prepares daily lunches of lentils, vegetables, rice, chapatis and salad for her husband, Chandrashekhar Chiplunkar, who runs the foreign exchange division of Oman International Bank. “The old fashioned, inexpensive dabbawalla system is a rare survivor in this fast-paced world.”

The Chiplunkars are loyal customers of 64-year-old Mr. Chowdhury. Like many fellow dabbawallas, Mr. Chowdhury is a migrant from a rural village in the region, still illiterate but having learned on the job to read the numbers and letters painted on the lunch boxes and to sign his name to customer receipts.

“This is the best profession for somebody like me in Mumbai,” Mr. Chowdhury said, pausing from his rounds, which consist of walking up and down winding staircases in old Mumbai apartment blocks, carrying food-laden containers in the morning and returning empty ones later.