After his arrest, Mandelstam was exiled to Cherdyn, only allowed to return to Moscow in May of 1937. During the Great Purge, Mandelstam refused to adopt Social Realism, causing him to be attacked by the public. In addition to being attacked, he was accused of having anti-Soviet views, causing more conflict for the poet.
After months of attack, Mandelstam was arrested in 1938 and charged with "counter-revolutionary activities". His sentence was to serve five years in correction camps. The poet was to transported to a Siberian transit camp to serve the duration of his sentence.
Mandelstam did not finish his sentence due to his death in a transit camp near Vladivostock on December 7, 1938. There are many supposed causes of death, including: heart failure, typhus, and insanity.
Life in exile had its issues, including lack of food, work, and communication with friends and family. As for the correction camps in which the poet was imprisoned, the conditions are unclear but one can infer the brutal and inhumane conditions based onthe result of his stay.
Sources:
Kipreyeva, Alyona. "Prominent Russians: Osip Mandelstam". <http://russiapedia.rt.com/prominent-russians/literature/osip-mandelstam/>
<http://www.spartacus.schoolnet.co.uk/RUSmandelstam.htm>