This feature is available if your IMAP4 server supports subscribing and unsubscribing to folders. When you unsubscribe to a folder, it no longer displays in your list of folders under the IMAP4 server, even though it is still in your IMAP4 account. This is especially useful if you are accessing an NNTP account through an IMAP4 folder.
Click Accounts > Account Options.
Click the IMAP4 account, and then click Folders.
Click the All tab to see all the folders in this account.
or
Click the Subscribed tab to see the folders you are currently subscribed to.
If you want to list folders containing specific text in the folder name (instead of listing all of the folders), type the text in the Search for Folders Containing text box, and then click Search.
Click the folder name, and then click Subscribe.
or
To unsubscribe to a folder, click the folder name, and then click Unsubscribe.
Click Close.