Under the Configuration menu, find Scan Configs

now either

Find an existing config that you use and select the “Clone” button to the right of it. After doing that, select the Edit button to the right of the new configuration
-or-
Select the Edit button of a config that you have already cloned from a default config

IF you just cloned it, you may want to change the name, say from “Full and fast Clone 1” to “My Full and fast”  Make the name something you will remember. You can also adjust the comment

Scroll down until you see “Network Vulnerability Test Preferences” If there are no items beneath that item, click on the icon on the right that looks like a folder with a Plus sign

Scroll down to “SMTP Settings From address:” scroll to the right and click the edit icon (looks like an open end wrench)

In the new window, you will have to scroll down and find the From address, Third party domain and To address. Update as needed.

Click Save in the lower right corner of the window

Wait for the Save button to stop its little bar graph of progress.

Hit the Save button again and you are complete!