[EX2013] Default folder is missing

Use the steps below to confirm that you are facing this issue, and to reset the PR_ATTR_HIDDEN property of the affected folder.

1. Download and extract the MFCMAPI tool from http://mfcmapi.codeplex.com.
2. Launch mfcmapi.exe and click OK through the intro screen.
3. On the Session menu, click Logon.
4. Select the Outlook profile for the affected mailbox, and click OK.
5. Double-click the email address which represents the desired mailbox.
6. In the left pane, navigate to the affected folder using the appropriate steps below for the type of Outlook profile you are using.
   
   Cached Mode
   
   1. Expand Root - Mailbox
   2. Expand IPM_SUBTREE
   
   
   Online Mode
   
   
   1. Expand Root Container
   2. Expand Top of information Store
7. Locate and select the folder that appears missing in Outlook, and check the value of the PR_ATTR_HIDDEN to determine if it is set to True, as shown in the following figure:
   
   
   
8. If PR_ATTR_HIDDEN shows a value of True, right-click the PR_ATTR_HIDDEN property and select Edit Property.
9. Uncheck the Boolean checkbox and click OK.
10. Close all MFCMAPI windows, and restart Outlook.

While you are looking at the folder properties you should also check PR_ATTR_SYSTEM. Its default value is also False, so if you find it currently set to True, after completing steps 1 through 9 above, you should change this value as well, using the additional steps below.

1. If PR_ATTR_SYSTEM shows a value of True, right-click the PR_ATTR_SYSTEM property and select Edit Property.
2. Uncheck the Boolean checkbox and click OK.
3. Close all MFCMAPI windows, and restart Outlook.

https://support.microsoft.com/en-us/help/2992093/