WinQuerySendMsg returns the first message sent from any window on a specified thread to any window on another specified thread, but has not yet been processed by the receiving window.

#define INCL_WINMESSAGEMGR /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HAB      hab;          /*  Anchor-block handle of the caller. */
HMQ      hmqSender;    /*  Message-queue handle of the sender. */
HMQ      hmqReceiver;  /*  Message-queue handle of the receiver. */
PQMSG    pQmsg;        /*  Pointer to the message structure. */
HMQ      hmq;          /*  Queue handle of the sender. */

hmq = WinQuerySendMsg(hab, hmqSender, hmqReceiver,
        pQmsg);