After an initial synchronization when the Vault Cache is first enabled, synchronization can start in the following ways:

• The Enterprise Vault Outlook Add-In automatically performs Vault Cache synchronization once a day. If the Outlook Add-In cannot connect to Enterprise Vault, then it waits for a minimum of five minutes before it attempts to contact the server again.

  If a scheduled synchronization time is missed, the Outlook Add-In attempts a synchronization when the user next opens Outlook. The first attempt is made after the period specified in the Exchange Desktop policy, in the Vault Cache advanced setting Pause interval.

  For example, users may miss their scheduled Vault Cache synchronization times during a weekend, when they do not use Outlook. In this case, a large number of header synchronization requests may occur at around the same time on Monday. To avoid an excessive load on the Enterprise Vault server, an Enterprise Vault mechanism limits the number of header synchronization requests that are accepted. When this mechanism operates, scheduled synchronization succeeds for some users. Other users have to wait until their header synchronization request is processed. The mechanism is invisible to users, so they do not see any error message. Their header synchronization request is repeated, as usual, at minimum intervals of five minutes until it succeeds. When the synchronization succeeds, the daily scheduled synchronization time is reset to the time of the successful synchronization.

  Alternatively, you can use the registry setting, OVAllowMissedMDCSyncOnStartup, to configure the Outlook Add-In to ignore missed scheduled Vault Cache synchronizations when the user opens Outlook. If you enable this setting, a Vault Cache sychronization occurs at the next scheduled sychronization time.

• If Vault Cache synchronization is required at other times, the user can start the synchronization in Outlook. A manual synchronization does not affect the next scheduled time for automatic synchronization.

  Unlike a scheduled synchronization, a manual synchronization that fails is not retried.

• You can use the Virtual Vault advanced settings Threshold number of items to trigger synchronization and Threshold total size of items to trigger synchronization to trigger an automatic Vault Cache synchronization. The settings specify thresholds for the number and total size of pending archive items in Virtual Vault.

  These threshold settings are important if your users move or copy items from their mailboxes into Virtual Vault to archive them. When only scheduled synchronization and manual synchronization are in use, items are probably not archived until the scheduled time. Until then, moved and copied items exist only on the user's computer. The threshold settings let you control when synchronization occurs, so you can minimize the risk of data loss.

  By default, the threshold settings are not active. You can optionally set one or both of them. If you set both, the first threshold value that is reached or exceeded triggers a synchronization.

  If the user suspends Vault Cache synchronization and either of these threshold settings is active, the user cannot move or copy items into Virtual Vault.

  Unlike a scheduled synchronization, an automatically triggered synchronization that fails is not retried.

  See Threshold number of items to trigger synchronization (Exchange Virtual Vault setting).

  See Threshold total size of items to trigger synchronization (Exchange Virtual Vault setting).