Three categories of people can work with Yahoo! Business Email plans: owners, administrators, and users.
Owner: An owner is the individual who purchased a Business Email plan. The Owner ID is the Yahoo! ID under which the plan was purchased. There can only be one owner of a plan, and owners can never be removed.
The owner is the default administrator of a Yahoo! Business Email plan.
Administrator: Administrator access can be assigned by the Owner or by an existing Administrator.
Administrators cannot remove the owner of the Business Mail plan and, unlike owners, they may not change plans. Administrators must have web access and an existing email address associated with the domain they wish to administrate.
Important: Once a mailbox User has been made an Administrator, that Administrator can delete or initiate changes for any email address associated with that plan (except that of the Owner). Choose your administrators well!
Owners and administrators may assign administrative privileges to a mailbox user while creating or editing a new email address; see How do I create a new mailbox? for more information.
User (member): A user holds an email address and a mailbox with which to access mail sent to that address. Users have no control over a Yahoo! Business Email plan.