In a Tuesday evening decision, U.S. District Judge Lucy Koh in San Jose, California, said the claims, including those on behalf of users of Google's popular Gmail service, were too dissimilar to be grouped together. She also said the plaintiffs cannot pursue their broad-based class action again.
A class action could have exposed Google to billions of dollars of potential damages and added pressure on the Mountain View, California-based company to settle.
Instead, email users might now be forced to sue individually or in small groups, lowering recoveries and boosting costs.
The case has been closely watched for guidance on how technology companies that provide email services might collect data used to target advertising, and perhaps boost revenue and profitability.
Sean Rommel and Jerome Tapley, lawyers representing the plaintiffs, did not respond on Wednesday to requests for comment.
Gmail users accused Google of violating federal and state privacy and wiretapping laws by scanning their messages so it could compile secret account profiles and target advertising.
Claims were also raised on behalf of students at schools that use Gmail, and people who do not use Gmail but communicate by email with people who do.
The lawsuit sought damages of $100 per day for each email user whose privacy was violated.
Google has said its software simply looks for keywords that can lead to the tailored advertisements.
Matt Kallman, a Google spokesman, said: "We're glad the court agreed that we have been upfront about Gmail's automated processing."
'PANOPLY' OF DISCLOSURES
In September, Koh rejected Google's effort to dismiss the lawsuits on the ground that users implicitly consented to its activity, recognizing it as part of the email delivery process.
But in Tuesday's decision, Koh said an assessment of whether users gave that consent required a broad review of how they came to know that interceptions were taking place.
"There is a panoply of sources from which email users could have learned of Google's interceptions," she wrote.
"Determining to what disclosures each class member was privy and determining whether that specific combination of disclosures was sufficient to imply consent ... will lead to numerous individualized inquiries that will overwhelm any common questions," the judge added.
In denying the class certification motion with prejudice, Koh said it would be unfair for Google to keep litigating.
She said Google has opposed such motions for 2-1/2 years, and had no chance to oppose in writing a recent request by the plaintiffs for permission to refile such a motion.
Google also faces litigation in California accusing it of violating federal wiretapping law by accidentally collecting emails and other personal data while building its Street View mapping program.
The case is In re: Google Inc Gmail Litigation, U.S. District Court, Northern District of California, 13-md-02430.
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