From the Overview: "The inbound ballot process covers everything that takes place from the time ballots are brought back to the counting facility by ballot collection teams or delivered by USPS [United States Postal Service], until the ballots are permanently sealed in storage containers for the retention period. This includes ballot receiving, ballot verification, ballot preparation, ballot scanning, ballot tabulation, and post-election audits. Although state laws vary on how soon before the election each part of the process can begin, there are some advanced considerations regarding purchasing equipment and building procedures. One of the most important components of the inbound ballot process is having a system to track ballots as they move from one processing area to another to account for any changes in the overall quantity. This guide outlines considerations for a typical inbound ballot process in a high-volume mail ballot environment."
U.S. Election Assistance Commission: https://www.eac.gov/