Energy = Mass x Speed of Light Squared ??

Astrophysics tells us that not only is the universe expanding, but that it is accelerating, due to the effect of Dark Energy which is said to comprise 74% of the mass of the universe. With unbridled acceleration, we are told that our view of galaxies will start to "blink out" in time as they reach the speed of light, an obvious consequence of eternal acceleration. What will actually happen however, when a mass like a galaxy reaches a speed that Einstein tells us will result in infinite mass. I know this is a big universe, but won't something of "infinite" mass be a problem?