1. Apparatus for redirecting messages in a publish/subscribe messaging system, the apparatus being operable to: receive a first message at an entity of the messaging system that is configured to receive messages for publication on a message topic specified in the received messages, the first message comprising a predetermined message element indicating that the first message is not a message for publication and instead comprises an instruction to redirect messages for a source message topic to a target message topic; record, by the entity, the instruction to redirect messages for the source message topic to the target message topic according to the first message; responsive to receiving, at the entity, a second message for publication on the source message topic, identify the recorded instruction to redirect messages for the source message topic to the recorded target message topic; and responsive to identifying the recorded instruction, perform: publishing, by the entity, the second message to subscribers of the source message topic and; redirecting, by the entity, the second message by publishing the second message to subscribers of the recorded target message topic, wherein when redirecting the second message to the target message topic according to the identified instruction, a message source indicated in the second message is aliased by replacing the indicated message source with an indication of the target message topic, thereby causing the published second message to indicate that the second message emanated from the target message topic instead of from the source message topic.