

The Synchronization errors and issues in Outlook 2019, 2016, or 2013 usually occur due to damaged or corrupt Outlook data files, i.e., OST (Offline Storage Table). But sometimes, you may experience synchronization issues in Outlook that can lead to errors and prevent users from sending or receiving new emails. With proper settings and configuration, the synchronization between the Outlook client and mailboxes server ensures uninterrupted email flow. Any changes made, such as drafting a new email or deleting messages, etc., are stored in the Offline OST file and synchronized with the mailbox server. When configured with an IMAP-based email account, Outlook creates an OST Outlook data file to store an offline synchronized copy of mail items, such as emails, contacts, attachments, notes, tasks, etc.

Signing in and out of the iCloud should enable the addin, but there could be something else preventing it from loading. If none of the above works, verify the iCloud addin is enabled in File, Options, Addins. This in only needed if you are going to stop using the iCloud. If you are asked if you want to backup the calendar and contacts locally, choose No. If the iCloud is not syncing with Outlook, open the iCloud control panel and sign out, then sign back in. The error should be gone when you sign back in. If the 'you need to repair the install' error comes up the first time you run iCloud, close Outlook and sign out of iCloud.
