Within a domain, EPA supports four types of mailboxes that are distinguished by their Preferences Set characteristics.
EPA-Exempt Mailbox (EXM) - for which no defined, associated Preferences Set exists and which is not located in a domain in which a Default Preferences Set is defined.
EPA-Standard Mailbox (ESM) - for which a defined, unshared associated Preferences Set exists.
Group Administrator's Mailbox (GAM) - whose user shares and administers a Preferences Set which is associated with one or more mailboxes.
Group Member's Mailbox (GMM) - whose user shares a Preferences Set which is associated with two or more mailboxes.