Open up the Vault Admin Console and go to "Policies -> Exchange -> Mailbox", find the exchange policy that your users use.
Double click the policy (or right click and go to properties)
Click on the Archiving Rules tab:
What do you have this set to? Based on Age, Based on Quota or Based on Age and Quota?
What do you ahve the rest of the settings set to? especially the "Never Archive Items Younger Than" setting
Also are you telling it to only archive items with attachments? this is listed on the same page aat the bottom
Next click the Archiving Actions:
What are these set to? Archive Unread Items by default is unchecked, however some users (i am guilty of this) of just accumulating stupid amounts of unread messages, and if this policy requires the items to be read, then they just never get archived.
Also the Create Shortcut is another one to look out for, if this is unchecked and Delete Original is unchecked then items will be archived, but the email in the mailbox will be left intact, so the items remain in the store as any other email
The problem is though, that you then have a large mailbox and its difficult to determine what items should be archived and what items have already been archived, and you may see a large group of items that will not archive again because they've been stamped to say they've been archived already etc
Now click the "Message Classes" tab
This is an important one, any of these message classes unchecked means it won't be archived.
So if you have same IPM.Note* unchecked, it means regular email won't be archived
If you wish to be archiving calendar items, make sure that you have IPM.Appointment* checked, otherwise they will be ignored
A large amount of items accumulate in a mailbox and they tend to be calendar items, people don't usually do a good job of going back and getting rid of really old appointments especially with large attachments
That being said, go to the "Advanced" button
First one is Archive Deleted Items folder, this is by default set to "Off" so any items sitting in the users Deleted Items, regardless of age, size, message class will not be archived, and this can account for a large bulk of mailbox size, plus if you are using Mailbox Archiving for psuedo compliance reasons, you should probably be archiving email that users might want to delete
Next there is the Archive Exchange Managed Folders, introduced in Exchange Server 2007, you could give everyone defined folders that have their own retention set there, so an exchange admin could give everyone a folder such as "1 Year" and users could put their email there and Exchange would not automatically delete the email for 1 year etc
By Default Enterprise Vault has a setting of "Managed" meaning it will archive the items there but automatically create a retention in Enterprise Vault that matches that of the Managed Folder, so if the Exchange Admins have given the managed folder a retention of 180 days or something like that, EV will read that, create a 180 day retention category and any item it archives will also be given that 180 day retention category
There is an option to be "Off" however which means that Enterprise Vault will simply ignore the folder, when it determines a folder is managed it will simply skip it, so no items in that folder will be archived at all, if this is set and your exchange admins have applied a managed folder policy against \Inbox, then it is possible EV is just ignoring the majority of your email because thats what its been told to do.
The setting most admins prefer is "Normal" so Enterprise Vault treats it just like any other folder.
Other settings you want to look at in this advanced colum are
Archive Unexpired Calendar Events
Do Not Archive Pending Reminders
Maximum Message Size To Archive In MB
Strip Attachments for non shortcut Items
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