Emails download to local IMAP account using Outlook 365 then disappears

I installed a user's email account using the secure IMAP settings (SSL) on a brand new computer using Win 10 Pro and Outlook 365. The emails and folders began to sync. When the sync is complete about 9 months of emails from the inbox is missing. I can see the emails for that period of months download during the sync process. The sent emails however, show up for that period. When I login using Webmail there are 2 options to check emails > Horde and Roundcube. When I login to Horde there are 4000 emails. When I Login to Roundcube there are 2000 emails. Is there a central location the mails are delivered to and Horde and Roundcube just displays the emails? If this is the case something is not right on the server's end. I deleted the profile on the pc and installed the email over and am getting the same result. The server is Centos 7.8 v86.0.18 The storage format for new accounts is maildir. It is possible that this account was transferred over using mdbox. Possible the database that stores these emails are corrupt? How can I check. Any ideas what else to look for a possible solution?