The United States Postal Service will suspend regular mail deliveries, retail services and administrative office activities this Wednesday, December 5th, to commemorate the National Day of Mourning declared for the late President George H.W. Bush, who died late Friday night.

Out of respect for the 41st President of the United States and to honor his vast contributions to our country during his lifetime, and consistent with the Presidential Proclamation, the United States Postal Service will suspend regular mail deliveries, retail services and administrative office activity on Dec.  5. We will provide limited package delivery service on that day to ensure that our network remains fluid and we do not experience any impacts to our package delivery operations that might negatively affect our customers or business partners during the remainder of our busy holiday season.  - USPS

According to USAToday, a National Day of Mourning is:

Days of mourning are recognition given to a select few — in the U.S. usually commanders in chief — and involve memorial activities, flying of flags at half-staff and other remembrances.

USAToday says when President Gerald Ford died in 2007, "the federal government was shuttered and financial markets were closed."