Question : Outlook 2007 IMAP not saving sent email to IMAP "Sent" folder

My clients depend on IMAP to save sent messages to the IMAP sent account.
This intermittently breaks, and the sent messages are saved instead to the "Sent Items" folder under "Personal Folders". Why? And how can I fix this so it is dependable? (500 pts because I can't find info of use on this anywhere.)

Windows XP or Vista
Outlook 2007
Private email service provided by "Rackspace"

Answer : Outlook 2007 IMAP not saving sent email to IMAP "Sent" folder

Rackspace has suggested that I try using SSL and see if that solves the problem.