4.85M accounts from Dangdang (dangdang.com) were exposed in this breach. Besides email addresses, it included some other data.
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Email addresses
In 2011, the Chinese e-commerce site Dangdang suffered a data breach. The incident exposed over 4.8 million unique email addresses which were subsequently traded online over the ensuing years.
Source: Have I Been Pwned (CC BY 4.0)