With half of all e-mail now estimated to be unsolicited spam mail, California is getting tough with Gov. Gray Davis signing the nation’s strictest anti-spam law on Tuesday.

A key provision of the law is that unsolicited mail can’t be sent to anyone who doesn’t "opt in" to the mailing. In the past, the mail could be sent unless a recipient had "opted out." This is a key difference to those who use e-mail to market everything from prescription drugs, discount travel, low mortgage and insurance rates to pornography. Beginning January 1, it will be illegal to send these e-mails to California addresses or to originate unsolicited marketing messages from California e-mail addresses.

The law includes $1,000 penalties for each unsolicited message and up to $1 million in fines for each marketing campaign.

"It turns basically everybody who hates spam into the enforcement authority," Ray Everett-Church, chief privacy officer for the consulting firm ePrivacy Group, told SiliconValley.com. "Not everyone will go down to the courthouse, but you'll get enough of us old cranks who will that we can make it too financially dangerous for spammers to continue."

The law could be moot however if anti-spam legislation passes in Congress—many say the law under consideration is weaker than the California law.

Thirty-five states have some sort of anti-spam law in place. The Wall Street Journal reports that until the California law was enacted this week, Delaware had the strictest law, which included the "opt-in" language.

California’s is made tougher through provisions that allow Internet providers, the state attorney general or citizens to sue the sender of the unwanted mail. Despite the law, no one expects to stop the spam, which experts say costs industry millions of dollars in lost productivity each year.

"Spam and scams aren’t going to go away tomorrow because of the passage of this law," Everett-Church told SiliconValley.com. "This sets a clear bar, though, for what's legitimate e-mail business. Scams will have to be next."