It also says, "Migrated data is available in New Outlook and can be accessed in On My Computer".
Is this a legitimate Outlook message?
I too had the same question as it prompts me every time I open Outlook for Mac. I was happy to see a few months ago that it had imported my archived mail from legacy. But as for this message I do not trust it for fear that I will lose 10 plus years of mail that I routinely refer to.
Here is how I do it.
In legacy I created folders called Archive Mail In and Archive Sent Mail in "On My Computer" (I did this years ago). Then I applied a rule to my inbox and sent box to move mail older than 90 days to the two folders I created in legacy under on my computer.
Because I work mostly in the new Outlook now, those rules only work when I switch back to legacy and apply them manually. The new Outlook will eventually update. Sometimes if I can't find what I need in new Outlook, I switch to legacy and find it there. I agree with other posters, the search in new Outlook is quite clunky.
But I still will not delete alleged duplicate data.
I hope this helps someone.
Rick