I assume you're using DFM to generate email messages about device state. If so, you can restrict the number and type of email messages being sent, but you will not be able to adjust the format or content of the messages.

If all you are about are messages which indicate if a device is up or down, go to DFM > Notification Services > Event Sets, and check the box next to OperationallyDown under the 'A' column. Then go to DFM > Notification Services > Notification Groups and create a new group. Select the devices for which you wish to receive notifications, and check the Critical and Information boxes under Event Severity, and check the Active and Cleared boxes under Event Status. Select A from the Event Set pull-down. Then complete the wizard.

Finally, go to DFM > Notification Services > E-Mail Notification, and add a subscription to your newly created Notification Group.

You should now only receive emails when a device generates an OperationallyDown event, and when that event clears.