Yahoo will give users of its free web-based email service access to unlimited storage capacity starting in May, according to a post on a Yahoo blog.

The capacity upgrade, timed to mark the 10th anniversary of the launch of Yahoo Mail in 1997, will not be available to all users at the same time. The upgrade will be rolled out users over a period of several months, wrote John Kremer, the vice president of Yahoo Mail.

The announcement ups the ante for rival Google, which rolled out its Gmail service several years ago with an initial capacity of 1GB per user. That capacity has steadily expanded over time and now exceeds 2.5GB. Google’s Gmail service is now available to everyone in the UK.

"We hope we're setting a precedent for the future. Someday, can you imagine a hard drive that you can never fill?" Kremer wrote. Yahoo Mail users now have a maximum capacity of 1GB for their mailboxes, which was raised in 2005 from 100MB.

While holding out the promise of unlimited storage capacity for Yahoo Mail users, Yahoo appears to have defined limits for how users can use the storage capacity of their inboxes. In his post, Kremer noted that Yahoo has developed "anti-abuse limits" for users.

Kremer's post did not detail what those limits will be.