Using classic Outlook for Windows in business environments
I have had the same issue, called Apple support, had a case number, but no resolution yet.
Since it is a yahoo account, I have been working on the Yahoo web site that still displays all my past emails.
Have tried rebuilding a couple of times in Outlook the inbox, but no success.
One of the thing that I have not tried yet, but I saw some people in forums saying that it worked for AOL, is to delete the account, recreate it, but NOT as a specific AOL, or Yahoo options, as "another" account, but you might need some help when doing that from the AOL or yahoo desk, and I have not had the time to try, but was curious if anyone had, and if it worked.
It is super annoying to only have 10,000 emails in Outlook, hopefully Apple can solve this one quickly
Luc