When organizing email, there are times when a user will create sub-folders for their email Inbox. Therefore, the folder structure would look something like this:
In the above example, you can see sub-folders added to the Inbox, and even a couple of sub-folders of sub-folders (e.g., Office Subscriptions under Microsoft). From a Web interface perspective, this is a perfectly acceptable way to organize emails.
However, when attempting to synchronize these folders with a third-party email client such as Apple Mail or Outlook, problems arise. This is because virtually every email client handles the synchronization of these sub-folders differently. From a mail server perspective, this makes it difficult to account for every mobile and desktop email client. Therefore, SmarterMail is unable to support synching sub-folders of a user's inbox with third-party clients. While you can create sub-folders of the Inbox and access them via webmail, you will not be able to use an email client and have access to these folders. While some may work just fine when using something like Apple Mail, it's very likely none of the sub-folders under an Inbox will sync properly.
NOTE: Folders and sub-folders created OUTSIDE of a user's inbox WILL synch properly.