Originally Posted by TigerShark

Each of the Notification categories has a matching entry in the registry
They can be found in HKEY_CURRENT_USER/ControlPanel/Notifications.

Each of the Notification categories has an "Options" parameter and a "Duration" parameter.

The "Options" parameter defines what should happen during the notification.
The "Duration" parameter defines the duration in minutes that the LED should flash.

Here is a list of the notification options:

Notification flag Value Description
NOTIF_SOUND 0x00000001 Sound notification.
NOTIF_VIBRATE 0x00000002 Vibrate notification.
NOTIF_FLASH 0x00000004 ROM notification.
NOTIF_MESSAGE 0x00000008 Message notification.

For both Email and SMS I have the Options set to 7 and the Duration set to 3000. So looking at the notification list above
7 = NOTIF_SOUND(1) + NOTIF_VIBRATE(2) + NOTIF_FLASH(4).

As you can see, I have disabled the NOTIF_MESSAGE. This was because the LED would stop flashing once the popup message on the phone went away. You can play with these values to see what works best for you.