Each account in the business can be one of three different service levels. The main difference between each service level is storage limits and cost.
- Basic - 500 MB email, 100 MB files (eg documents) - $15/y
- Standard - 2 GB email, 1 GB files (eg documents) - $30/y
- Professional - 25 GB email, 10 GB files (eg documents) - $60/y
- Enterprise - 150 GB email, 60 GB files (eg documents) - $300/y
Additionally, Professional accounts can have "personal" domains and aliases. The only difference between personal domains and business domains is who can manage the domains. For business domains, they're managed on the Manage -> Domains screen, and can be managed by any administrator of the business. For personal domains, they're managed on the Options -> Own domains screen by the particular user that owns the domains.