ANSWER:

In Outlook 2010

“0 down vote

Go to File > Account Settings > select the account & click on ‘Change’. Click on ‘More Settings’ then ‘Sent Items’ tab. Then change from ‘Save sent items in the following folder on the server’, to ‘Save sent items in the sent items folder on this computer… Davsmg”

This will indeed keep a copy of the sent mail on the computer, but this folder is not synced using IMAP.

by Kevin from http://superuser.com/questions/407409