The decision by US District Judge Lucy Koh in San Jose, California, means people who emailed with Yahoo Mail subscribers since October 2, 2011, may now sue as a group under the federal Stored Communications Act for alleged privacy violations, Reuters reported.
Holders of non-Yahoo Mail accounts have accused Yahoo of copying and then analyzing their emails in order to create "targeted advertising" for its estimated 275 million Yahoo Mail subscribers.
Search and display advertising is a major money-maker for Yahoo, generating 79% of the company's revenue in 2014.
The plaintiffs estimated that the nationwide class of non-Yahoo Mail subscribers has more than 1 million members, Reuters reported. They are seeking an injunction barring the alleged interceptions, as well as damages.
A Yahoo spokeswoman said the company cannot comment on ongoing litigation.
Lawyers for Yahoo unsuccessfully argued in court that some plaintiffs actually consented to its activity by continuing to email Yahoo subscribers even after learning how the company used the information.
In March 2014, Judge Koh denied class-action status to Gmail and non-Gmail subscribers in their case against Google Inc. because she said it was difficult to determine which users consented to the company's activity.
She distinguished the Google case from that of Yahoo.
"Yahoo may have to, as a practical matter, adjust its scanning practices on an individual basis," Koh wrote. "That does not, however, change the fact that plaintiffs seek uniform relief from a common policy that Yahoo applies to all class members."
