The receiving application responds with a positive WM_DDE_ACK message if it can honor the request, otherwise it responds with a negative WM_DDE_ACK message.

The data portion of the WM_DDE_ACK message, in either case, must contain the original command string. The requesting application compares the command string in the acknowledgement to its original request to determine which request the acknowledgement is for.

The response is posted to the window handle specified in the first message parameter.