First, spammers won't honor it. They routinely commit US Federal crimes to deliver their crap; violating the do-not-email list wouldn't even put a hair out of place. We've already seen the IEMMC create a so-called "global opt-out lists" - and they use it to harvest the addresses and sold them off to more spammers. Rodney Joffe created a "legitimate" such list, and the DMA *and* all otehr spammers ignored it.
Second, the only acceptable "do-not-email" list consists of "*@*" - all addresses are opted-out by default.
Anyone sending bulk email to my servers had better be using proper, confirmed opt-in, or they will find I have opted them out by adding their entire IP space to the firewall deny tables.