A major challenge in identifying massive quiescent galaxies at z > 3 is distinguishing truly passive systems from dust-obscured star-forming galaxies, as both populations exhibit similar red ultraviolet-to-near-infrared colors. In this work, we present Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 continuum observations of five ultramassive galaxies (UMGs; log(M⋆/M⊙)>11 ) from the Massive Ancient Galaxies At z > 3 NEar-infrared survey, spectroscopically confirmed at zspec > 3. One UMG is weakly detected at 872 μm while the remaining four UMGs are undetected down to the 3σ depth. By incorporating ALMA constraints and far-infrared-to-radio photometry into the spectral energy distribution (SED) analysis, we demonstrate that all five UMGs are quiescent, lying significantly 1 dex below the star-forming main sequence. We estimate dust masses using both SED modeling and modified blackbody fitting, with consistent results between the two methods. Our results reveal...