Using older versions of Outlook for Mac for personal email and calendar
Hello Snig27,
Thank you for your reply and great effort on this case!
And sorry for delay my response since I was OOF in the past few days.
For this issue, I also had a test from my side, and the result is as same as that of yours. I've got over 10,000 items and tried to import to the New Outlook for Mac but only party of those emails have been imported. It seems a product bug for the New Outlook on Mac. We will proceed and have our engineers be aware of the this concern.
We recommend you to revert to the legacy Outlook for Mac for the time being.
Thank you for your time and cooperation and wish you have a nice day!