"Secrecy sleeves"—inner envelopes protecting the anonymity of a voter's ballot—aren't necessary in jurisdictions that have modern ballot-counting machines. But not all jurisdictions have had the funding to acquire the equipment. Sixteen states require that all mailed ballots be inserted into them.
With much greater volumes of mailed ballots expected in 2020, and many voters mailing ballots for the first time, the lack of a secrecy sleeve could invalidate unusually high numbers of ballots in some jurisdictions and influence outcomes in close races. There is national attention on Pennsylvania, where the state's highest court has mandated that "naked" ballots not enclosed in the required inner envelope should not be counted.