Read the following Microsoft Office article for more information: You can move the items using Outlook Web App client. In many cases, Outlook does work properly with folders as large as 5.000 items and more, but decreasing the folder size can improve the performance drastically, and generally this is the first troubleshooting step to be done in a case of slow/freezing Outlook client. The problem usually is not a connectivity issue between the mail client and the mail server, but rather a local Outlook database corruption. Sometimes Mac users report that Outlook 2011 /Outlook 2016 for Mac is not syncing properly (or syncing quite slowly, freezing frequently) with Exchange.
This article is intended to assist users in solving database corruption cases in Outlook 2011/Outlook 2016 for Mac when connected to an Exchange mailbox.
