The dormant email IDs are being released a month after the Sunnyvale, Calif., company notified users that they would have 30 days to log into an inactive account if they wanted to keep it.
People awarded the rights to the recycled email addresses will have a 48-hour period to activate the accounts beginning Aug. 15.
Yahoo is hoping the inactive IDs will be claimed by people who will use them to log into its website and discover a series of changes to its email, home page and other services that have been made since Marissa Mayer became the company's CEO a year ago.
The resurrection of inactive email addresses, however, could be exploited by computer hackers hoping to use the IDs to pry into sensitive information about the former accountholders. There's a risk because many people use their email accounts as logins at a different password-protected websites, including Facebook, Twitter and Amazon.com. That raises the specter of some people trying to use the recycled email IDs to request the passwords of former accountholders.
Yahoo says it has taken a series of security measures to minimize the chances of any mischief. Among other things, Yahoo says emails are now being bounced back from the inactive email accounts. The company says it has also developed a system that will help other websites identify email addresses that have been transferred to new accountholders after the recycling is completed.