[m_eiman]

The problem hasn't got anything to do with delivery notifications or auto-responders: if you need an answer right away you must use a synchronous form of communication, e.g. voice call.

iMessage, SMS, email et al are async by design. Until you hear or see an ack that's from the actual recipient (and not something automated by a device), you can't be sure the message has been properly received.

[GuiA]

iMessage has a "send read receipt" feature (deactivated by default).

[m_eiman]

Yes, but that doesn't mean the recipient actually read it - it means that iMessage is/has been the active application on at least one of the recipient's devices.