The United States Postal Service NEVER shuts down, their unofficial motto is:
"Neither snow nor rain nor hear nor gloom of night stays these couriers from the swift completion of their appointed rounds."
But, considering the extreme temperatures are to blame for at least 4 deaths int he midwest right now, they USPS decided to shut down to be safe.
Mail delivery has been halted in North Dakota, South Dakota, Nebraska, Kansas, Minnesota, Wisconsin, Iowa, Illinois, Indiana and Michigan.