Some background:
The United States Postal Service filed a proposed rule on May 29 that would prohibit absentee/mail-in ballots for general elections from being delivered to anyone not on a list provided to USPS by state election officials. The proposed rule was published in the Federal Register on June 2.
Under the rule, states would submit to USPS the names of absentee/mail-in voters, as well as "the unique barcode applied to the outbound and return ballot mail envelope for such individuals." States would be allowed to modify this list up to the final day for sending out absentee/mail-in ballots. The rule would not apply to primary elections or to military or overseas voters.