Yahoo Inc. plans to offer unlimited e-mail storage to its roughly quarter of a billion users, starting in May, it said on Tuesday. The world’s biggest e-mail service is scrapping its free e-mail storage limit of 1GB, or about a billion bytes of data, responding to explosive growth in attachment sizes as people share ever more photos, music and videos via e-mail.

Microsoft has a 2GB free e-mail storage limit, while Google caps its Gmail service at 2.8GB.

“We are giving them no reason to ever have to delete old e-mails,” Yahoo co-founder David Filo said in a phone interview. “You can keep stuff forever.”

Officials said the decision to remove e-mail storage limits reflects the plunging cost of storage as new personal computers store up to a trillion bytes of data and owners of 80GB iPods can carry 100 hours of video in their pockets. By contrast, when Yahoo first introduced its e-mail service a little under a decade ago, it capped individual storage at 4 megabytes per user. At that time, an “ultra high-density” floppy disk for personal computers then held 144 megabytes.

“People should think about e-mail as something where they are archiving their lives,” said Filo, who remains active in managing technical operations at the Sunnyvale, California, company and carries the honorific title of Chief Yahoo.

Starting in May, the changeover to unlimited storage should take a month, said John Kremer, vice president of Yahoo Mail.