A system for delivering messages to a receiver mobile device and a method and memory storing instructions therefor are described. The system comprises a key server arranged to: transmit a first signal responsive to receipt of a message from a sender mobile device; transmit a delivery confirmation notice responsive to receipt of a second signal from the receiver mobile device; transmit a key to the receiver mobile device responsive to receipt of the second signal from the receiver mobile device; and a message server communicatively coupled with the key server and arranged to: transmit a third signal to the receiver mobile device responsive to receipt of the first signal from the key server; transmit a fourth signal to the sender mobile device responsive to receipt of the delivery confirmation notice from the key server.