Header synchronization is always part of Vault Cache synchronization. The item header contains enough information to enable the item to be represented in Virtual Vault, or in offline Archive Explorer within Outlook. It also contains information to associate the header with the content of the full item.

Where changes have occurred in the online archive, Vault Cache synchronization downloads header information from the Enterprise Vault server and applies the changes to the Vault Cache.

Note that some changes within the mailbox do not take effect in the online archive until the next run of the Mailbox Archiving task. For example, a run of the Mailbox Archiving task is required when a user moves an archived item or creates a folder in the mailbox.

Changes to the online archive may potentially require Vault Cache synchronization to include content download as well as header synchronization, for example when an item is automatically archived. However, content download may not be necessary if preemptive caching is in use.

See Preemptive caching.

Where changes have occurred in Virtual Vault and therefore in Vault Cache, those changes are synchronized to the online archive.

Header synchronization also synchronizes any changes that are made to the folder hierarchy, either in the online archive or in Virtual Vault. Users cannot move, delete, or rename a folder in Virtual Vault if the folder exists in the mailbox. Users must perform the actions on these folders in the mailbox, in Outlook or OWA.