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One alternative is to subscribe to iCloud calendar with your Exchange/O365 email accounts or any Outlook account, and then sync the same accounts in Outlook for Mac. See details:
I love that this has been "Under Review" since June 09, 2017. While the alternative worked for my needs, sounds like having this officially supported - even with over 15K requests for this feature over multiple posts – is not a priority for the Mac Outlook Team.
Try the alternative, maybe it will work for you.
It is funny how this easily used to be done in Entourage with a script but cannot be done with all the "advanced features" in Outlook for Mac.
I'm shocked with the maturity of this product, this is still not an option.
While I can use the control+] and control+[ to move back and forth through the messages, just hovering my mouse over the button and clicking the NEXT button was much more productive with the previous version.
I have dozens of folders nested within dozens of folders to keep my mail organized and sorted based on over 200 incoming rules. I would like a better visual cue that there is unread mail in those folders (and subfolders) than a light number, which doesn't show for the parent folder.