Bugzilla

Courier and dovecot and probably others usually make Inbox the root folder with all other folders in the personal namespace (called "INBOX.") under Inbox. This can be changed at the server but that is typically unlikely unless the tb user controls the server. You can flatten the folder tree that tb shows so Inbox and the folders that were under inbox are now at the same level by setting advance server setting "IMAP server directory" to "INBOX" (no quotes). It seems to be case sensitive since just "inbox" doesn't have an effect. Make the change and collapse and expand the server's tree and/or restart tb. This changes the tree to flatten the folders to the Inbox level. 

So this seems to be mostly fixed as originally described in comment 0 above and in several dups.

Maybe the fact that the server directory must be set to INBOX (uppercase) for this to work is still a bug, not sure. (IMAP treats mailbox INBOX as case insentivite.) However, since servers report the personal namespace as INBOX, maybe it makes sense for the server directory to also be set to the exact same string to show INBOX's sub-folders at INBOX's (root) level.

One other observation: Once the tree is flat and if you create a folder under Inbox, tb physically creates Inbox/Inbox/newFolder but it appears to be just under Inbox. Then if you remove INBOX from the "server directory" setting, collapse/expand and view the folders again, you see a "gray" Inbox (greyed)/newFolder under the toplevel Inbox. Probably not a big problem but some might consider this a bug.

Courier and dovecot and probably others usually make Inbox the root folder with all other folders in the personal namespace (called "INBOX.") under Inbox. This can be changed at the server but that is typically unlikely unless the tb user controls the server. You can flatten the folder tree that tb shows so Inbox and the folders that were under inbox are now at the same level by setting advance server setting "IMAP server directory" to "INBOX" (no quotes). It seems to be case sensitive since just "inbox" doesn't have an effect. Make the change and collapse and expand the server's tree and/or restart tb. This changes the tree to flatten the folders to the Inbox level. 

So this seems to be mostly fixed as originally described in comment 0 above and in several dups.

Maybe the fact that the server directory must be set to INBOX (uppercase) for this to work is still a bug, not sure. (IMAP treats mailbox INBOX as case insentivite.) However, since servers report the personal namespace as INBOX, maybe it makes sense for the server directory to also be set to the exact same string to show INBOX's sub-folders at INBOX's (root) level.

One other observation: Once the tree is flat and if you create a folder under Inbox, tb physically creates Inbox/Inbox/newFolder but it appears to be just under Inbox. Then if you remove INBOX from the "server directory" setting, collapse/expand and view the folders again, you see a "gray" Inbox/newFolder under the toplevel Inbox. Probably not a big problem but some might consider this a bug.