Wisconsin mail is not required to be postmarked, so SCOTUS's sua sponte addition of a postmark requirement for mail-in ballots means many ballots received on time won't be counted https://twitter.com/rickhasen/status/1248676659240120320

AFAIK, the only time requirement for mail-in ballots in WI is that they must be received by a certain date. B/c the dist court extended the date for receipt, SCOTUS invented the postmark requirement to limit voting to election day https://twitter.com/WSJMattD4/status/1247304424894185474

Interesting thread covering an ongoing discussion of this issue by the WI Election Commission https://twitter.com/srl/status/1248720766763401220