hmm - I've never used a subdirectory of contacts (just tried it out of curiosity, and couldn't get the contacts to export reliably). TBH I barely trust Outlook, mobile phones or anything else similar to reliably store important contacts (without splitting the email/phone numbers and other info), I grew up in the days when Filofaxes were still common and there are times when I seriously consider starting to use mine again..
@cweickhmann @daniel
its supposedly fairly straightforward (I did even export a CSV from my outlook to see if it worked, and I got a valid CSV file), but I haven't tried importing data yet as I don't want to risk hosing the data that is already in my profile (and its unclear what happens if there are any errors in the CSV file)
https://support.microsoft.com/en-us/office/import-contacts-to-outlook-com-285a3b55-8d93-4ac8-93df-43fffd13b2f1