Select Options from the Tools menu.

Click the E-Mail Options button.

Uncheck the box Save copies of messages in Sent Items folder. Click OK. As a last step, you need to set up a rule to save your sent mail in your sent-mail IMAP folder.

Select Rules and Alerts... from the Tools menu.

Click the New Rule... button.

Click the Start from a blank rule button. Click the line Check messages after sending. Click Next.

Click on the uses the form name checkbox. Click form name in the bottom half of this window.

Select Message in the left field. Click Add ->. It will appear in the right field as shown. Click Close. Click Next ->.

Check the box move a copy to the specified folder. Click specified in the bottom half of this window.

Select the sent-mail folder from your IMAP account. Click OK.

This window may pop up. Click OK.

Click Next.

There's nothing to change in this window. Click Next.

Name this rule sent-mail. Click Finish.

The sent-mail rule will now appear in your list of rules. If the checkbox is not on, there may be an error with the rule. Make sure you are online and get back to this Rules window later to make sure it can be turned on without an error.

Click OK.

IMPORTANT NOTE: If you ever see a message indicating that you lost your connection to the IMAP server while sending an e-mail, you will need to open the above window again to turn back on this rule. Outlook will turn off this checkbox if such an error occurs. If you do not turn this checkbox back on, all outgoing mail that you send will not be saved in the sent-mail folder.