Thank You
Part of the answer depends on what hosting provider you're using.
For example, if you use Gmail for both IMAP and outgoing SMTP,
you probably do *not* want your "sent" folder stored on the Gmail
IMAP server. I recommend that you ask your hosting providers what
they recommend and then do that.
For most hosting providers -- but not Gmail -- you probably do
want to store your special folders on an IMAP server so they will
be accessible from any IMAP client on any machine. I've written
some thoughts about sent messages here:
Server-Side Sent Messages
<http://deflexion.com/2006/05/server-side-sent-messages>
Hope this helps,
Nancy