The IMAPISession::GetLastError method returns a MAPIERROR structure containing information about the previous session error.
HRESULT GetLastError(
HRESULT hResult,
ULONG ulFlags,
LPMAPIERROR FAR * lppMAPIError
);
The IMAPISession::GetLastError method retrieves information about the last error that was returned by an IMAPISession method call. Clients can provide their users with detailed information about the error by including this information in a dialog box.
You can make use of the MAPIERROR structure pointed to by the lppMAPIError parameter, if MAPI supplies one, only if GetLastError returns S_OK. Sometimes MAPI cannot determine what the last error was or has nothing more to report about the error. In this situation, GetLastError returns a pointer to NULL in lppMAPIError instead.
For more information about the GetLastError method, see Using Extended Errors.