When you compose your Email message, tap Options in the top toolbar.
The expanded Email message options are shown.
From the Receipt: drop down menu, select the type of return receipt you'd like to request.
The drop down menu show the following options:
None: No receipt is returned.
Read: Receipt is returned when the Email message is read.
Delivery: Receipt is returned when the Email message is delivered.
Delivery and Read: Receipts are returned when the Email message is both read and delivered.
When your recipients get your Email message, they will be asked to verify that they've read it.