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A user called in, complaining that they were unable to create a new folder in a shared mailbox. The error message they got indicated that the folder already existed. I started troubleshooting the issue, and it transpired that they had created the folder already, though it did not show up. I tried a number of fixes, including restarting Outlook, removing the mailbox from account settings, and even deleting their mail profile altogether. It was this last attempt that would lead me to the correct solution.
It turned out that the mailbox was very large indeed, comprising literally hundreds of folders, and just shy of twelve gigabytes of data. By default, our profiles are set up to use cached Exchange mode, with all options enabled. Among these options is the option to download shared folders, which is all well and good when the shared folder is a few hundred megabytes. Once you start dealing with major folder structures, however, at some point Oulook simply says “enough is enough”, and stops caching. It does not, however, indicate that there is more data to be accessed.
The solution to the issue, then, was to disable the setting. It is found at File > Account Settings > Account Settings > Profile > More Settings > Advanced:
By disabling the “Download shared folders” setting, and restarting Outlook, all the folders – including the one my user had originally called about – were available.