When you have many folders with many messages in Microsoft Outlook synchronization can be slow or even appear to hang.
This happens because Microsoft Outlook downloads all messages every time including attachments while with a normal email IMAP application only headers are synced.
To solve this issue in Outlook, please follow these steps:
- After setting up your IMAP email account in outlook, right click on your email account and select “IMAP Folders…”
- Click on the “Subscribed” tab and click the “Query” button.
- Select all items in the list as follow:
- Select the first item in the list and scroll all the way down.
- Hold shift and click the last item in the list.
- Click the “Unsubscribe” button.
- It may prompt about folders that cannot be unsubscribed, just click “OK” here.
- Next, select the "ALL" tab as we are now going to sync folders we wish or need to sync.
- Select “Drafts” and click subscribe.
- Select “Inbox” and click subscribe.
- Select “Spam” and click subscribe.
- Select “Sent” and click subscribe.
- Select “Templates” and click subscribe.
- Select “Trash” and click subscribe.
- Do this for any other folders you wish to sync with the server.
- Uncheck the option “When displaying hierarchy in Outlook, show only subscribed folders.” at the bottom of the window.
- Click “OK” to close the window and apply the changes we just made.
This will SHOULD resolve extremely slow synchronizations with Microsoft Outlook.
The issue can still be noticed if you have a very large Inbox folder, Sent folder, Trash folder, or any subscribed folder. The recommended method of avoiding this Outlook issue is to simply file away messages from these subscribed folders into archived / unsubscribed folders (this also keeps you email organized!).
Or even better you can simply auto archive messages in outlook to clean them out of your mailbox.
Lastly, be sure to empty the Trash folder frequently enough to avoid a constantly growing Trash folder.