Answered on January 24,2018
I-ticket refers to the ‘Internet Ticket’. I-ticket can only be booked at least three days before the journey date. It is required to book I ticket three days before because IRCTC needs at-least three days to deliver the booked i ticket at your address by the courier. Whenever you book the I ticket IRCTC dispatches that ticket immediately within 2 hours to your mentioned address.
e-Ticket refers to the electronic ticket. It is also called as Digital ticket. E -ticket can only be booked online.