NEW YORK (CNN/Money) - If a list can help to block telemarketers, something similar should work for e-mail spammers, right?

Maybe, say anti-spam experts, who admit they have their doubts.

With more than 50 million phone numbers registered on the national do-not-call list aimed at telemarketers, the Senate unanimously passed a bill Wednesday that would create a similar measure to block unsolicited commercial e-mails.

The vote marked the first time the Senate has taken action against spam, which now accounts for about half of all e-mail traffic.

The Direct Marketing Association, the biggest group representing marketers, said it supported the effort in the Senate to create a national standard that distinguishes commercial e-mail from unlawful spam. But the group expressed concern about the provision that could lead to the creation of a national do-not-e-mail registry.

Furthermore, said DMA spokesman Louis Mastria, a do-not-e-mail list probably wouldn't work. "A do-not-spam list sounds attractive, but it won't work the same as do-not-call," Mastria said.

Spammers often send out e-mails containing pornographic and get-rich-quick schemes from their home computers or some off-shore terminals. "Tracking them down won't be easy," Mastria said.

"If they are breaking the law already, a new measurement will not prohibit them from sending those e-mails," Mastria added. "But it will be horribly painful to legitimate e-mail marketers."

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Matthew Prince, co-founder of Unspam, a Chicago-based consulting firm, said that while the bill might be a compromise, it's a good start.

"Parents we spoke to said children receiving inappropriate spam is a serious concern," he said. "Spammers should face enhanced penalties for sending inappropriate messages to children," and a do-not-spam list is "long overdue," he added.

Some experts expressed concern that the new bill isn't as strict as some of the state laws already in effect.

"We are a bit worried that this bill will pre-empt some tough anti-spam laws in states like California, Washington and Virginia," said John Mozena, co-founder of the Coalition Against Unsolicited Commercial E-mail.

Lawmakers in the Senate noted spam has become a priority among voters and could overwhelm the Internet if left unchecked.

Similar legislation in the House has stalled as lawmakers try to hammer out differences between two competing bills. The Bush administration has expressed support for the measure.