Yahoo! Business Email email users who follow normal email practices and comply with our anti-abuse controls can consume an unlimited amount of free email storage. This applies to both new and existing users.
However, the purpose of unlimited storage isn't to provide an online storage warehouse. Usage that suggests this approach is flagged by Yahoo! Business Email's anti-abuse controls.
Unlimited storage gives normal email account freedom from worrying about hitting a storage limit. You can save your correspondence and memories and never worry about deleting older messages to make room for more.