I ran in to this issue where Outlook 2016 for OSX said it required to be activated. Very annoying as I don’t have a 365 account and that is what it requires before you can use it. It seems that this problem was caused by the fact that I used an older version of the preview/beta in the past. It can simply be solved be taking the following steps:
- Open Terminal
- Type: defaults delete com.microsoft.Outlook
- Type: killall cfprefsd
- Exit the Terminal session and launch Outlook
This basically deletes all the current settings for Outlook and wipes the cache. Now you can enter your details again and it will all work as expected.