FEDEX or UPS. Or a local carrier.
This was a urination match between the GOP controlled legislature and the Democratic Governor. When the Governor could not get the date changed, I have little doubt that the word went out to the postal employee unions to take actions that will support claims that this was a faulty election. The FBI needs to looks at all electronic communications traffic in and out of the governor’s office in the relevant period before the election and all electronic communication to postal union representatives. This was election tampering. Likewise I would look at whomever was in charge of running the polling places in Milwaukee County. That also looked like a deliberate attempt to sabotage the administration of the election in order to facilitate post hoc challenges to its legitimacy.