To speed up the synchronization time for subscribed IMAP folders in Microsoft Outlook:
- Go to to Send/Receive, then Send/receive groups, and define send/receive
- On the right side of the send/receive groups window click on the Edit button
- Uncheck the "Get folder unread count for subscribed folders"
- Under Received mail items check the option "Use the custom behavior defined below"
- In the next window below select INBOX and leave the other folders unchecked
- Click OK and then exit out of your options
- Do a send/receive to verify your Outlook is faster now