Despite no documentation stating there is a limit for Mac 2011, it’s apparent that reducing mailbox size can drastically improve performance and minimize downtime. Keeping them under 5,000 or so items seems to keep things in shape. Namely, the inbox and sent items folders. Item Count Limitation: One of the biggest culprits (seemingly) is the high number of items users tend to have in their mail folders. Here is where this article will come to your aid. Various reports from numerous forums (both Microsoft and non-Microsoft) indicate a variety of ways to combat this. Why this pertains to Outlook 2011 on the latest supported version of Exchange (2010) is unknown, but the existence of the issue is undeniable. There is no “official” Microsoft documentation stating this but older documentation for Exchange 20 explains issues regarding mail store parsing by mail clients. The problem is a communication issue between the mail client and the mail server. The issues vary from mail not syncing at all to delayed and intermittent mail retrieval from the Exchange server to mail disappearing and just about everything in between. There have been numerous cases reported of Outlook 2011 for Mac not syncing properly with Exchange (bis NOT supported by Outlook for Mac).