Source: Microsoft Internal
Have you ever wanted to send e-mail notifications with the high importance flag set?
It's possible but you have to start your favorite XML editor ;-)
Modifying Microsoft.SystemCenter.Notifications.Internal MP XML to Support Email Priority/Importance
Once the new management pack is active, recipients should see subsequent email messages from subscriptions that use the modified write action modules display the new priority attribute.
You can also support priority levels for non-MS clients using the X-Priority header with a numeric value, e.g. <Headers><Header><Name>X-Priority</Name><Value>5</Value></Header></Headers>.
This is tested this in our lab using the SP1 RC and RTM builds of SCOM 2007. The mail clients used for testing were Outlook 2003 and Outlook Express 6.