There is no “official” Microsoft documentation stating this but older documentation for Exchange 20 explains issues regarding mail store parsing by mail clients.

Why this pertains to Outlook 2011 on the latest supported version of Exchange (2010) is unknown, but the existence of the issue is undeniable.

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Before emptying the cache, you may want to ensure that your Outlook information is backed up.

If you successfully connected to the account before, try to connect to it from another Exchange application, such as Outlook Web App.

Resolution 1: Clear Offline Items Most Exchange account configured in Outloook has Cached Exchange Mode enabled by default to allow user to continue working with Outlook when offline in addition to improve the performance.

When the items in Outlook is mismatched with online version, the cached items may be corrupted.

Various reports from numerous forums (both Microsoft and non-Microsoft) indicate a variety of ways to combat this. Item Count Limitation: One of the biggest culprits (seemingly) is the high number of items users tend to have in their mail folders. Keeping them under 5,000 or so items seems to keep things in shape.

Despite no documentation stating there is a limit for Mac 2011, it’s apparent that reducing mailbox size can improve performance and minimize downtime.

No new mail activities or even download progress on Inbox, but the other folders at least updating upon selecting.

I can see about 23K mails when I check the synchronization through the inbox properties.

The content and emails in the mailboxes are not refreshed, i.e.