https://www.vice.com/en_us/article/wx88xm/here-are-the-extraordinary-measures-the-usps-plans-to-get-your-ballots-in

The USPS says it will authorize "extraordinary measures" to deliver ballots by their respective state deadlines up to and through Election Day, including checking every residential mailbox for a ballot and putting ballots in Express Mail rather than regular First-Class mail. 

But to keep the USPS honest, plaintiffs in one of the many lawsuits against the USPS regarding election mail have proposed a court order that, if implemented, would require the USPS to implement these measures in the 22 districts with an election mail on-time delivery rate of less than 90 percent rather than merely saying it will do so. There are 67 USPS districts across the country.