Outlook - IMAP Sent Items folder not keeping the sent items
If you have set up the above rule you may want to stop Outlook automatically copying your sent messages to your local Outlook Sent Items folder as well as the IMAP Sent folder. To do this:
1. Choose Tools > Options
2. Click on the Preferences tab, then E-mail Options
3. Uncheck the Save copies of messages in the Sent Items folder box.
4. Press OK