Is there such thing as a "do not mail" list? If it is possible to opt-out of private (tele)marketing and block spam, then logically it should be possible to opt out of this service too.
There is: https://www.dmachoice.org/. It took quite a while (several months) until I noticed any changes, but my (very subjective) impression is that the (spam) mail volume decreased over time.
Another thing I'd suggest is https://donotcall.gov/. Registering there seems to have had a positive impact on the number of spam calls I receive.
