A system and method for messaging in which, when a connection to a queue manager (220) is established, the queue manager allocates a Connection Identifier from the same name space (300) as Message Identifiers and returns this information (400) to the user. The user can then use this Connection Identifier as a Correlation Identifier, safe in the knowledge that it will not clash with any system generated Message Identifier or Correlation Identifier. A secondary benefit to this allocation scheme is that if a shared reply queue suffers from a build-up of messages then the Correlation Identifier in those messages can be used to identify the application expected to receive those messages.