An apparatus for delivering a message from an originating subscriber to a target subscriber across a communication network comprising; means for receiving in a first network a message from an originating subscriber to a target subscriber and an identifier of the target subscriber, the target subscriber being associated with the first network and the originating subscriber being associated with a second network, the message and identifier being received from the second network; means for identifying at least one network node associated with the target subscriber and being responsible for delivering messages to the target subscriber; means for selecting a network node from the at least one network node for delivery of the message; means for receiving from the second network an allowed time period for delivery of the message; means for determining the expected delivery time of the message for the selected network node; means for comparing the expected delivery time with the allowed time period for delivery; and means for forwarding the message to the selected network node for delivery to the target subscriber in dependence on the allowed time period exceeding the expected delivery time.