When you have many folders with many messages in Microsoft Outlook, synchronization can be slow or even appear to hang.
Outlook hangs because it downloads all messages every time, including attachments, while with a regular email IMAP application, only headers are being synced.
To solve this issue in Outlook, please follow these steps:
Next, select the “ALL” tab as we are now going to sync folders we wish or need to sync.
The steps above should resolve the issue of Outlook hanging on “Fix Outlook hangs on synchronizing subscribed folders.”