From the Overview: "Election officials expanding the use of absentee or mail voting must continually work to ensure that voter data is accurate. An incorrect name, address, or signature on file for a voter may result in that voter not receiving a ballot on time or at all, or their voted ballot not being counted. [...] Inaccuracies in address records can result from voter actions or omissions, such as moving to a new address without providing notice to election officials, or they can be caused by other factors, such as data entry errors. An initial mailing to voters, sent well before mailing any ballots, can give election officials an early indication of existing issues with their records and offer an early opportunity to clean up potential errors. This initial mailing could serve the dual purposes of explaining any coming changes to voters--including any COVID-19 [coronavirus disease 2019]-related changes--and exposing potentially problematic addresses for election officials. It can also inform voters displaced because of COVID-19 (e.g., people living with family/friends, in care facilities) that they need to update their voter registration information, such as temporary mailing address."
U.S. Election Assistance Commission: https://www.eac.gov/