This means spammers can no longer use open relays without permission. It doesn't mean you should cancel your subscriptions to blacklist services that detect and prohibit incoming messages from open relays, but at least those services that target "legitimate" spammers will become more effective because it will be easier to identify the legitimate solicitors.
More on the Minus Side
The legislation may ultimately prove ineffective, because it puts even informed end users in a catch-22: It requires recipients to opt out of future mailings if they don't want to be contacted again, but how can you opt out if you don't answer? Suddenly, after training ourselves to simply delete unsolicited e-mail because spammers interpret even negative responses as positive, we're supposed to respond to every single message, opting in or opting out.
In a recent Washington Post column, Bill Gates advised against responding to spam unless you're absolutely sure the sender is legitimate. Given the new legislation, Gates should have advised users to respond to every piece of spam.
Meanwhile, by responding, we're telling the senders that we do, in fact, read their mail, which encourages them to add our names to the lists they sell to other spammers. To make matters worse, most users don't have a clue how to determine whether a sender is legitimate, so they're spammed if they do and spammed if they don't.