Sent items folder is not showing for the user from Outlook and OWA.
Folder may visible if user use OWA light version..
This apply for Outlook folders such as: Junk Folder, Deleted Items, etc..
PR_ATTR_Hidden attribute for Sent Items folder was set to true
1) Install MFCMAPI then close Outlook.. You can download MFCMAPI from http://mfcmapi.codeplex.com/Release/ProjectReleases.aspx?ReleaseId=35656
2) Click on the Session menu and select “Log on and Display Store Table”. (This prompts you for your Outlook profile)
3) Double click on your mailbox in the top pane. It will open new box, if it is not open, just right click on your mailbox store and click open store..
4) Expand Top of IPM_SUBTREE then find and select the sent items folder - Check for PR_ATTR_HIDDEN attribute.