Using older versions of Outlook for Mac in business environments
I agree that this isn't an OS X 10.10.3 issue or an hosted Exchange issue.
I am getting the same type of popups with our on premises Exchange 2010 server and with an Exchange 2013 server.
This is a bug in the Outlook 2016 15.9 update in the way Outlook is trying to get the certificate information.
It appears that when Outlook 2016 is validating the certificate, it uses the root domain instead of the actual server name used for connectivity.
For example, if your ActiveSync or Outlook Anywhere server is webmail.mydomain.com, 15.9 will try to use mydomain.com. Prior to 15.9, it would use webmail.mydomain.com.
Besides, the constant crashing, I'm going to uninstall Outlook 2016, 15.9 and reinstall a prior version.
Just my two cents,
Paul K