Microsoft makes it hard for people to move from their Entourage program data to modern Outlook for Mac.
Entourage was the email/calendar/contacts part of Office for Mac. Office 2011 replaced it with Outlook 2011 for Mac.
Outlook 2011 had a conversion option that let former Entourage users move to the new software.
That was dropped from Outlook 2016 for Mac, leaving Entourage users with a conversion problem.
(Microsoft’s saved some development costs on Outlook 2016/Mac by dropping Entourage migration. It suited Redmond to arrogantly assume that everyone who had Entourage/Office 2008 had already moved to Office 2011).
Moving from Entourage 2008 to Outlook 2016/Mac
The annoyingly long-winded way to switch from Entourage 2008 to Outlook 2016 for Mac is to use Outlook 2011!
Install Outlook 2011 (Office 2011) on the computer, import and convert the Entourage data.
Then install Office 2016 for Mac to replace the Office 2011 software.
Downloading Office 2011 for Mac
Microsoft will let you download Office 2011 for Mac IF you have a valid product key from an earlier purchase.
If you don’t have an Office 2011 product key, maybe ask around your Mac friends.
Office 2011 for Mac isn’t available from Office 365
From 22 September 2016, Office 365 subscribers can’t download and install Office 2011 for Mac.
CDN Content Delivery Network
But all it not lost … Microsoft provides a curious alternative download page until 10 October 2017.
Scroll down this page to see a download link to Office 2011.
It’s unclear if this download requires a product key. Perhaps, without a key, it will run in a trial mode that’s enough to convert Entourage data?
While you do this round-about conversion you can thank Microsoft for wasting your time.