The smaller OST has persisted since and, as I write, it’s about 600MB smaller than the Outlook 2010 version.Such a wonderful reduction warranted further investigation, so off I went to find out.

To make Outlook download only the headers of large messages automatically:, Outlook will only download the headers information for messages exceeding your threshold size.
But getting the full emails is easy, as is deleting messages right at the server without downloading them in full ever.
The sync activity is shown on the “Local Mailbox” tab.
The Microsoft Exchange Connection Status reveals more about Outlook’s current synching process.
It also only displays “To monitor Outlook’s synching processing more closely, you can open the Microsoft Exchange Connection Status dialog.
To do this, hold CTRL when clicking on the Outlook icon in the Notification Area and then select Connection Status…First things first – If the mailbox is auto mapped i.e.doesn’t show in this list: You may need to remove and re-add the permissions using Exchange Online Powershell, specifying Auto Mapping to be : Then after removing the Shared Mailbox from Outlook, add a new account to the single profile.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.You can set up Outlook to download only the subject, sender and other minimal data for big messages automatically.