The USPS would never offer that feature. They get directly paid [1] to deliver that spam, so providing you a 'cutoff' method directly effects their bottom line

The USPS would never offer that feature. They get directly paid [1] to deliver that spam, so providing you a 'cutoff' method directly effects their bottom line because the sender will not want to pay for items that never get delivered. But I do agree, it would be a nice feature to have a "no junk mail" switch that could be turned on. [1] I believe they do not charge a high enough price for the junk, but they do get paid to deliver it in any case.