Outlook-iPhone and private email How can I send private email from my iphone to an Outlook user so his delegates cannot see the email?
You can setup the permissions of the Delegate so they can not see private items. Here's a KB article about granting permission to them:

http://support.microsoft.com/kb/249324

The trick is now finding a way to get your iPhone to add the "Private" flag to your message. I don't have an iPhone so I can't help you there. Just edit the properties of your message and see what you can change.