Exchange Server 2003 recipients can be mailbox-enabled users, or mail-enabled users, contacts, public folders, or groups.
Deleted Mailbox Retention and Deleted Item Retention are used to provide extra protection against inadvertent deletions, keeping you from having to restore from backup.
Storage limits can be configured on individual mailboxes, on individual mailbox stores, or by mailbox store policies that can be applied to multiple mailbox stores.
Access to distribution groups and address lists can be limited through permissions.
Multiple storage groups can be used to implement different backup schedules.
A storage group can contain five mailbox or public stores, and a single server can contain up to four storage groups.
Recipient policies are used to apply e-mail addresses to the users that match the filter.
A single offline address list can make multiple address lists available offline, and a storage group uses the same offline address list for every mailbox store in the group.
A single set of transaction logs exists for all mailbox stores in a storage group, but each mailbox store has its own database files.