Microsoft officially announced that MS Outlook 2011 will not work at all with El Capitan. It crashes when synchronizing with an Exchange server. No date of a fix yet. https://support.microsoft.com/en-us/kb/3098396 Shortly after you start Microsoft Outlook for Mac 2011 on Mac OS X El Capitan (version 10.11), Outlook hangs when it tries to sync with the server. The Spinning Wait cursor is displayed, and the application status is displayed as "Not Responding." Workaround: To work around this issue, run Outlook for Mac 2011 on Mac OS X Yosemite (version 10.10) or an earlier version. Why did Apple release an OS that does not work at all with the widest-used email client and server in the world? Did they do any QA testing whatsoever? i'm pretty certain that every QA hack in the entire universe knows to test against MS Office. "Oops! We forgot to see if MS Office works?" What kind of utter nonsense is that? Is it possible to uninstall El Capitan? Do I have to roll back using Time Machine?