If you’re planning to upgrade to OS X El Capitan and you use Outlook 2011 to get email from Microsoft Exchange, you may want to delay upgrading. On El Capitan, connecting to Exchange email servers causes Outlook 2011 to freeze and display a beachball cursor.
The issue appears to only affect Outlook 2011 when configured to access Exchange servers. When set up with only IMAP accounts, Outlook 2011 does not appear to display this behavior.
Microsoft is aware of the issue and has posted a knowledgebase article about it:
https://support.microsoft.com/kb/3098396
