Introduced in MSMQ 3.0. Gets the message's lookup identifier.
Assembly: System.Messaging (in System.Messaging.dll)
The property provides read-only access to a message's lookup identifier. The lookup identifier, introduced in MSMQ 3.0, is a 64-bit identifier that is generated by Message Queuing and assigned to each message when the message is placed in the queue. The lookup identifier is not the same as the message identifier that is generated when the message is sent.
Message Queuing generates a lookup identifier for all messages that are placed in any queue, including application-generated destination, administration, and report queues, as well as system-generated journal, dead-letter, connector, and outgoing queues. In other words, this includes both messages sent by sending applications and by Message Queuing. The lookup identifier is unique to the queue and has no meaning outside the queue.
If a message is sent to several destination queues, or if a copy of a message is stored in a computer journal or queue journal, each copy of the message will have its own lookup identifier when it is placed in its respective queue.
The property can only be read on messages retrieved from a queue.
A lookup identifier is used to read a specific message in the queue. Once the lookup identifier of a message is known, the receiving application can call the PeekByLookupId or ReceiveByLookupId function to go directly to that message and peek at or retrieve it from the queue, unlike cursors that must start at the front of the queue and navigate towards the end of the queue,
Obtaining the lookup identifiers of the messages in the queue is the responsibility of the application. One possible way to obtain the lookup identifiers is to create a trigger for the destination queue that invokes a component that caches the identifiers of each message as they are placed in the queue.