How did you get it to work? My Exchange accounts wont auto-discover properly, and El Cap has removed the "sever settings" tab in calendar preferences->accounts, for example (used to be in between "account information" and "delegation"), so I can't edit settings manually as I could in Yosemite to work around auto-discover.
I honestly don't know. I don't know if it's something to do with my Exchange server as my experiences with Outlook 2011 under El Cap appears to be different to others reports. It beach-balls every time I launch after 5 seconds...
When I was looking around about 2 weeks ago I realised I had my Exchange account under 'Internet Accounts' in 'System Preferences'. I must have added this previously, or it's sync'd from a mobile device. Turned it on and it's been rock solid since then and both Mail and Calendar syncs fine.
I do know that my company supports auto-discovery, that I didn't manually enter the settings, and that it appears to be working properly.
I know none of this helps... sorry!