Microsoft Outlook will by default save your sent mail in a local folder called "Sent Items". That sent mail is not accessible to you from another computer and it is not backed up on our mail server. You can create a rule to make Outlook copy sent mail up to an IMAP folder of your choice where it will then be available to you from other locations:

Create a Rule

1. On the Tools menu, click Rules Wizard, and then click New.
2. Select Start from a blank Rule.
3. Click to select Check Messages After Sending, and then click Next.
4. Click to check the "on this machine only" check box and then click Next.
5. Click the "Move a copy to the specified folder" check box.
6. Click to select the "specified" folder in the Rule Description box.
7. Click to select your Sent Items folder on the server. Click OK, and then click Next.
8. Click Next again, and then specify a rule name. Click Finish, and then click OK.

Because Outlook thinks the "Sent Items" IMAP folder is just a normal folder it will display the From field rather than the To field (meaning you can't see who you sent the message to). To fix:

1. Open your IMAP Sent Items folder. Right click on the column header (for example, Subject).
2. Choose "Customize Current View". Click Fields.
3. Scroll down to "To" and click Add. You can move "To" up or down the list to, normally you would want it near the top.
4. Click "From" on the list on the right and click Remove.

As an added step you can tell Outlook to stop saving a local copy of the sent mail. This is an optional step.

Disable Save Sent Items in the Sent Items Folder
1. On the Tools menu, click Options.
2. On the Preferences Tab, click E-mail Options.
3. Click to clear the "Save copies of messages in Sent Items Folder" check box
4. To close the dialog boxes, click OK twice.