Here is the excerpt from the admin help, you can search on "Using report mode to test archiving" and find these in the help.
The report gives, for each mailbox, the following details about the items that would be archived on a real run of the Exchange Mailbox Task:
System Name
Mailbox name: On Exchange 5.5 systems this is the distinguished name of the mailbox. On Exchange 2000 systems this is the legacy distinguished name.
Associated NT account: This is the primary Windows account for the mailbox.
Mailbox state: One of the following: New, Enabled, Disabled, Suspended.
Date: The date the mailbox was checked.
Start time: The time the check started.
End time: The time the check finished.
Number of archivable items: An archivable item is one that Enterprise Vault will archive when the item meets the archiving criteria. An archivable item must be one of those listed in the message classes that Enterprise Vault will archive automatically.
Enterprise Vault has a number of standard message classes that it will archive and you can add more as necessary. To view or change the Enterprise Vault message classes, view the properties of the Enterprise Vault Directory and click the Advanced tab.
Total size of archivable items: The total size of items that Enterprise Vault will archive when the items meets the archiving criteria.
Number of archivable folders: The number of folders in the mailbox from which Enterprise Vault will archive.
Number of items ready to archive: An item that is ready to archive is an archivable item that meets the archiving criteria and thus would be archived on a real run of the Exchange Mailbox Task. Depending on the number, it could take more than one run of the Exchange Mailbox Task to archive this number.
Size of items ready to archive: The total size of items that would be archived on a real run of the Exchange Mailbox Task. Depending on the number, it could take more than one run of the Exchange Mailbox Task to archive this number.
Number of large items: The number of items that are larger than the Start with items larger than setting on the Site Properties: Mailbox Rules property tab. These items that are archived before all others.
Total size of large items: The total size of items that are larger than the Start with items larger than setting on the Site Properties: Mailbox Rules property tab. These are items that are archived before all others.
Number of messages that would be archived: The number of message that would be archived on a single, real run of the Exchange Mailbox Task.
Size of messages that would be archived: This is the total size of items that would be archived on a single, real run of the Exchange Mailbox Task.
Quota limit: Shows the mailbox storage limit.
Quota used: Shows the used percentage of the mailbox storage limit.
% of Quota free: Shows the unused percentage of the mailbox storage limit.
Number of Expired Shortcuts: The number of shortcuts within the mailbox that are ready to be deleted, according to the criteria you have set on the Shortcut Deletion tab in Site Properties. For more information, see Expiry and Deletion.
