INBOX, Inbox, and MS Outlook 2007

[T T]

Hello list,

I have a Cyrus-IMAP server with altnamespace:yes and unixhierarchysep:
yes. I want my sent messages to be stored on server, the INBOX.Sent
being the most obvious choice. Setting this in Apple Mail was easy
(Mailboxes>Use this folder for...>Sent). With Outlook 2007, however,
I've run into a strange problem.

The Outlook documentation suggests:
" ... In the Internet E-mail Settings dialog box, click the Folders tab.

Folders tab in Internet E-mail Settings dialog box
To choose a custom folder for saving your sent items, click Choose an
existing folder or create a new folder to save your sent items for
this account in."
(http://office.microsoft.com/en-us/outlook-help/change-where-sent-e-mail-messages-are-saved-HA010164216.aspx)

OK, I choose Inbox.Sent, but the sent messages are still saved in a
local Outlook folder. If I try to move them to Inbox.Sent, I get an
error message: server said the mailbox does not exist. Yes, what does
exist, is INBOX.Sent, and both SquirrelMail and Apple Mail store sent
messages there. Now, if I create a subfolder in Inbox.Sent, like
Inbox/Sent/test, it DOES exist from the server perspective (and sent
mail can be stored there). But  Inbox/Sent still cannot be used for
that, and INBOX.Sent is not visible in any folder list.

The most bizarre is that Outlook recognizes the existence of
INBOX.Sent by storing its own test messages there (those generated
while creating the account).

After googling half a day I'm out of wits. Please, help.

Thanks.

Tom