How do I create sub-folders (nested folders) in Thunderbird?

Subfolders (nested folders) allow you to organize your mailboxes in multiple levels of folders. This can be helpful in sorting and managing large numbers of mailboxes.

When you use the New Folder... command in Thunderbird, by default it creates an actual mailbox within your IMAP folder or your Local Folders. You cannot add a subfolder to a mailbox.

To nest folders within your IMAP directory on the server:

1. Click once on the secure IMAP account name (username@math.ias.edu) and select New Folder.
2. To create a master (top-level) folder, enter the name of the new folder -- followed immediately by a forward slash (/)- ( Example: Mathematics/ ) -- and create it as a subfolder of username@math.ias.edu. The new mail folder's name will appear in italics.
3. Then, right-click on that folder's name in the IMAP account list and choose New Subfolder.

Notes: The expandable folder itself cannot contain mail, only sub-folders (which can themselves contain mail).