A question arose the other day, which is worthwhile covering here. The question is :
When using Outlook 2007 or Outlook 2010 Instant Search, with Virtual Vault enabled, what is meant to be searched?
To answer this you need to consider what you are truly looking at within Outlook when you have Virtual Vault enabled. Virtual Vault for all intents and purposes is the MDC file, one file.. with “stub” information in it of all the items in your archive. Even if you have no vault cache content stored locally, or if you have size limitations, or date limitations, the MDC, the metadata, is always the complete set. It contains things like dates, times, subject, recipients, and most importantly the first 120 characters of the message.
When you search with Outlook Instant you have the following options (From Outlook 2010) :
All mail items
All Outlook Items...