MAPI_LOGON_UI
const mapi.MAPI_LOGON_UI;A dialog box should be displayed to prompt the user for logon information if required. When the MAPI_LOGON_UI flag is not set, the calling client does not display a logon dialog box and returns an error value if the user is not logged on. MAPI_LOGON_UI and MAPI_PASSWORD_UI are mutually exclusive.