Aggressive efforts to protect e-mail users from spam are blocking many legitimate business messages from reaching consumers.

Return Path, a New York e-mail research firm with an engineering and marketing office in Superior, said Tuesday that Internet service providers are blocking as many as 37 percent of “opt-in” e-mails.



Those are messages that customers have agreed to receive, such as newsletters or airfare updates.



The company studied 30,000 e-mail marketing campaigns to arrive at its figures, said Jennifer Wilson, Return Path vice president of marketing.



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