As anonymous indicated, use the "Send email to all users of role." I believe roles are identified by number. If you go to /admin/people/permissions/roles, and hover over 'edit permission,' the number at the end of the url should indicate the id for the role.
In Rules there's a "Send email to all users of a role" action you can use for this purpose. There is no "Send to" input for this action because all you need to do is specify the role, not the email addresses.
The event 'User has logged in' puts into context the user entity for the user who has just logged in. The user entity by itself has no fields. The user entity with added fields is known as a bundle.
To expose the fields of the bundle to Rules you need to use the 'Entity is of bundle' condition. This condition takes three inputs:
The specific entity you are ...