We are on nt, but here's our fix:
Uncheck "In folders other than the Inbox, save replies
with original message."
NOTES:
-- This problem occurs only with Replies (and perhaps
forwarded messages).
-- If user prefers to keep that option checked, they just
need to understand that the items ARE being sent, and that
they can simply move them to Sent Items if they wish.
FURTHER INFO:
In the Microsoft Knowledgebase, there is an article
(305090) which reads: "When you reply to a message...,
the reply message appears to be stuck in the Outbox.
However, the message is sent.
It goes on to say: "This behavior occurs when you select
the In folders other than the Inbox, save replies with
original message check box."
If you do really want that option checked, go ahead and
turn it back on. Those replies turning up in your Outbox
do not appear to be a problem, so long as you understand
that they have truly been sent, and that moving them to
the Sent Items folder (if I understood this part of the
problem correctly) will send them again. However, I'm
thinking that I did misunderstand that part, so perhaps
moving them to the Sent Items folder is not a problem.