Click Tools > Rules and Alerts > New Rule. In Outlook 2003, choose Start from a blank rule. select Check messages after sending, and click Next.
Check defer delivery by a number of minutes in the next dialog box, click a number of in the lower pane, and clear the number of minutes to delay
Remember : The maximum is 120.
Click OK and then Next.
Check except if it is marked as importance in the list of exception options, click importance in the bottom pane, choose High in the drop-down menu that appears
Click OK, and then Next.
NOTE: Supply a name, review its settings and click Finish