If you're having issues with Outlook not syncing mail folders, there are several steps you can take to try and resolve the issue:

How to fix outlook not syncing with folders? 

1. Check your internet connection: Make sure you're connected to the internet and that your connection is stable. Poor internet connectivity can cause syncing issues in Outlook.

2. Check your Outlook settings: Verify that your Outlook settings are configured correctly. Go to "File" > "Account Settings" > "Account Settings" and check that your email account is listed and active. If you see any errors or issues, try reconfiguring your account settings or removing and re-adding your email account.

3. Check your folder settings: Ensure that the folders you're trying to sync are set up for synchronization. Go to "File" > "Account Settings" > "Account Settings" > "Change" > "More Settings" > "Folders" and make sure that the folders you want to sync are selected.

4. Check your email provider's settings: If you're using an email service like Gmail or Yahoo, check their settings to make sure that IMAP is enabled and that the folders you want to sync are selected.

5. Clear the Outlook cache: Clearing the Outlook cache can often resolve syncing issues. Go to "File" > "Options" > "Advanced" > "Outlook Data Files" > "Offline Settings" and click "Clear Offline Items". This will delete any cached data and force Outlook to re-sync with your email server.

6. Check for updates: Make sure that your version of Outlook is up to date. Check for updates by going to "File" > "Office Account" > "Update Options" and selecting "Update Now".

If none of these solutions work, you may need to contact Microsoft support for further assistance. How to delete mail folders in outlook.com?