To ask for a read-receipt, please press the 3-dots menu in the compose screen and choose Enable Read Receipt.

You can also set the this option as default by using Accounts | tap the account | Advanced Account Settings | Enable Read Receipt.

Please note that only recipients using email servers that support this capability at the other side such as Exchange servers will report back read-receipt messages to BlueMail.

Also, on some clients, the recipient has to approve before the read-receipt will be sent and acknowledge acceptance.