If Microsoft Office is one of your 'must haves', it might be wise to delay upgrading your Mac to OS X 10.11 El Capitan.
An unusually large number of people are reporting problems with Office 2011 and Office 2016 after upgrading to OS X 10.11 El Capitan.
The main symptom is that Outlook 2011 or Outlook 2016 crash on opening or after a period of use. When this occurs, other Office applications reportedly crash or freeze as well, suggesting that a piece of code shared across the suite is involved.
"We are aware of the issue with Outlook 2011 on El Capitan and of Office 2016 on El Capitan.
"We are working on a fix for 2011 and for 2016 we are working closely with Apple to resolve this issue as soon as possible. Unfortunately we do not have any timelines for either fix, please stay tuned and thank you for your understanding."
A MacInTouch reader named John Welch wrote "I've talked with some folks I know on that team - it's a very deep bug that only shows up in El Capitan, so they've got to fix it without breaking Outlook 2011 in 10.10 and earlier."
Paul Bassel added "Regarding the comment of disbelief that Microsoft had to have known about the problems Outlook 2016 has with El Capitan during the beta period, I, for one, sent them plenty of crash reports -- many times daily."
The Office 2016 for Mac September 23, 2015 Update provided "bug fixes and feature improvements to Microsoft Outlook 2016 for Mac" but it apparently didn't to the whole job. That update is available via Microsoft AutoUpdate for Mac.