Users get an error opening outlook of Cannot expand the folder. There is not enough memory available to perform the operation.

To resolve this issue by disabling the Download Public Folder Favorites option, follow these steps:

1. In Outlook, click File, click Account Settings, and then click Account Settings.
2. Select your Microsoft Exchange account, and then click Change.
3. Click More Settings.
4. On the Advanced tab, click to clear the Download Public Folder Favorites check box.
5. Click OK.
6. You are prompted to restart Outlook for these changes to take effect. Click OK.
7. Click Next, click Finish, and then click Close.
8. Exit Outlook, and then restart Outlook.

For more info see https://support.microsoft.com/en-gb/help/2968387/you-receive-insufficient-memory-errors-when-you-expand-a-mailbox-or-pu