In India, is there a requirement to have every traveler's passport in order to purchase airline tickets?
The name in the ticket must matches the name in the Passport, especially in international flights. Not only that, also passport information must be added to the reservation, such as expiry date, passport number and issuing state.
Is that necessary? The information is indeed necessary and can be sent in a message. However the copy is not. Unless he is buying the ticket from an agency that requires a photocopy of the passport for verification, or if he is a cyber thief intending to use the photocopy of your passport for evil reasons.
I'm not going to assume this is only for international flights out of India. For clarity, you don't need a passport or any other form of ID when booking; you only need either when you're actually at the airport and/or checking in.
Here are the scenarios:
For international flights to/from India
Yes, you do need a passport since this would be a requirement for clearing immigration in India and the destination.
For flights within India
No, you don't necessarily need a passport for flights within India. Other acceptable forms of ID are (from the Indian airline Indigo's website; note that these are government rules so it applies to all domestic flights):
- Valid Passport
- Valid Driving License
- Election Photo Identification Card
- PAN Card issued by the Income Tax department
- Photo Identity Card issued by the employer, being government and reputed private sector organizations
- Children should carry their school identification cards or any other photo identification proof along with them
- Valid birth certificates of Infant(s) needs to be produced at the time of check-in for age proof