One Chicago firm has setup a physical mail processing location in Wisconsin, just over the border from Chicago. Physical mail is being redirected there, scanned and the digital image sent to attorneys and staff working from home. This gets around the stoppage of physical mail delivery in population centers.
The United States Postal Services has a website location which indicates where there are business mail service disruptions due to Covid-19. As of the date and time of this comment, the USPS is experiencing minor service disruptions in 13 states and in Puerto Rico. The USPS reports there are no overall capacity problems.
https://about.usps.com/newsroom/service-alerts/business/welcome.htm
WE are scanning mail in house and have a secondary location at another office if needed.