EMA C++ RDM Usage Guide : 3 Login Domain : 3.2 Usage : 3.2.13 Login Post Message
 
3.2.13 Login Post Message
Open Message Model consumer applications can encode and send data for any item via Post messages on the item’s Login stream. This is known as off-stream posting because items are posted without using that item’s dedicated stream. Posting an item on its own dedicated stream is referred to as on-stream posting.
When an application is posting off-stream, the PostMsg requires Name and ServiceId information. For more details on posting, refer to the Enterprise Message API C++ Edition Developers Guide.