Overview

You have a situation where an Outlook for Mac user is not able to download all their emails. You have tried deleting their Outlook files completely and re-adding the account, but downloading emails is taking an extremely long/indefinite time. You may also see the message "Inbox: determining changes" on Outlook for Mac, with a blue bar moving between right and left. 

Solution

Before you take the steps below, please ensure that you have optimized the disk space by follow the steps mentioned in Reducing local macOS Outlook storage space, since Outlook for Mac occupies enormous disk space that can affect performance, responsiveness and synchronization of the macOS Outlook application.

If after optimizing storage space, Outlook for Mac is not syncing, this could be due to database or configuration files being corrupted. Please take the following steps: 

• Email synchronization issues can be resolved by clearing the Outlook cache on the user's PC. In order to do this, please see this Clear the cache in Outlook for Mac article by Microsoft.
  
  
• If the issue persists after clearing the Outlook cache, it is recommended to reset the user's profile from the server-side. To do this, kindly follow the steps below:

1. 1. Stop Kerio Connect.

   2. Navigate to the Kerio store folder.

      The default path (could be different if you changed it during install) for your server is: /usr/local/kerio/mailserver/store

   3. From the store folder, navigate to the user's folder: /mail/<user>/tr

   4. Make a backup of the following folder and files:

      • Folder: __keriomapi__STORE

      • Files: .journal.db and specguid.fld

   5. Remove the above folder and files from the user's folder in the Kerio store directory.

   6. Start Kerio Connect.

   7. Re-create the Outlook profile for Mac.
      
      For more information, see Outlook profile crashes, gives errors and not syncing all emails

Please note that backing up and removing the files on the server (as mentioned above) will only affect that individual user and whichever accounts they have set up with KOFF (Outlook for Windows) or EWS (Outlook for macOS). Devices connected via IMAP/POP3 or Exchange ActiveSync (EAS) won't be affected. For the ones affected, you will have to recreate the Outlook profile.

Also if you are wondering about how all your Outlook clients will react when the older calendar data is suddenly removed, please be assured once they synchronize with the server, the client will delete their local copy as well.

Related article: You can refer to the following Microsoft thread regarding the warning message "Inbox: determining changes": Microsoft 365 Outlook for Mac - continually displays "determining changes" and will not display latest emails