In Jewish prayer YHWH is pronounced adonay (my Lord) because the ineffable name of god is too sacred to be uttered. In the days before 70 C.E., when the Temple was standing in Jerusalem, the tetragrammaton was pronounced only once a year, on Yom Kippur, the Day of Atonement, by the High Priest in the Holy of Holies of the Temple. How he pronounced it, no one knows. See Choon-Leong Seow, “The Ineffable Name of Israel’s God,” BR 07:06.