A client can send unsolicited data to a server by using the DdeClientTransaction function to send an XTYP_POKE transaction to a server's callback function.
The client application first creates a buffer that contains the data to send to the server and then passes a pointer to the buffer as a parameter to the DdeClientTransaction function. Alternatively, the client can use the DdeCreateDataHandle function to obtain a data handle that identifies the data and then pass the handle to DdeClientTransaction. In either case, the client also specifies the topic name, item name, and data format when it calls DdeClientTransaction.
The DDEML passes the XTYP_POKE transaction to the server, specifying the topic name, item name, and data format that the client requested. To accept the data item and format, the server should return DDE_FACK. To reject the data, the server should return DDE_FNOTPROCESSED. If the server is too busy to accept the data, the server should return DDE_FBUSY.
When the DdeClientTransaction function returns, the client can use the lpdwResult parameter to access the transaction status flag. If the flag is DDE_FBUSY, the client should send the transaction again later.
If a server does not support the XTYP_POKE transaction, it should specify the CBF_FAIL_POKES filter flag in the DdeInitialize function. This prevents the DDEML from sending this transaction to the server.