If Outlook is not showing mail folders into your account. it will become a really irritating issue for you. at such point of time. you must want to get it fixed as soon as possible. to fix these kind of errors. you have to make the following changes.
1. Please check the internet connection. make sure that the internet is working perfectly fine on outlook.
2. Go to the account settings, here you need to enable the cache for exchange servers.
3. Remove the current account and then re-add the mail account back into the outlook.