A method of modifying a data message during transmission through a data communications network, the data communications network being arranged to deliver messages under control of a network operator and including a first store-and-forward network node. The first store-and-forward network node is arranged to store data messages and forward the same to a recipient in dependence on status data corresponding to a terminal associated therewith. The method further includes receiving a message at a second store-and-forward node, wherein the second store-and-forward node is different from the first store-and-forward network node, arranging for the message to be modified before being forwarded from the second store-and forward node, and transmitting the message to the first store-and-forward network node for forwarding to the recipient.