Up until Outlook 2007, by default an IMAP account will indeed be set to “Download headers only”.With Outlook 2010, this default has changed to “Download complete item including attachments”.This file is also known as the offline data file which can be recognized easily when looking at the extension which is OST.By default the file is stored in The advantage of Cached Exchange Mode is that mailbox content is also available when you don’t have a connection to Exchange, excluded the new items which haven’t been cached.Additionally, Note: There is a bug in Microsoft Internet Explorer 4.01 that prevents this from working.There is also a bug in Microsoft Internet Explorer 5.5 that interferes with this, which can be resolved by upgrading to Service Pack 2 or later.

If you are using Outlook Connector, you can compact the local cache file to improve performance.By default, Outlook 20 cache the mail items in Shared Mailboxes.I’ve recently had a question from a colleague about solutions for using cached mode with very large (~10GB) shared mailboxes used by large numbers of users.Whether you use POP, IMAP, Active Sync or Outlook Connector, you can perform various tasks to improve Outlook’s performance.Follow the steps outlined below to keep Outlook running like a well-oiled machine.