immediate recipient
Computing term for the direct or intended recipient of a message, packet, or data transmission, as opposed to a relay or broadcast target.
The immediate recipient of this message is the department manager.
Please do not open this email unless you are the intended recipient.
受信者 is a general term for any receiver, while 対象受信者 specifically refers to the intended or immediate recipient in a computing context.
Compound of 対象 (target) + 受信者 (recipient). A technical term likely coined in computing contexts.