Welcome to NGA, Kristi!
Try going to "Your Profile" (the blue "head and shoulders" icon in the upper right corner of the home page.
Then "Change your site preferences".
Then the third row should be : "Private message e-mail notification?"
If you set that to "Yes, email me", you should get an email notification in your home email address when you get an NGA "Tree-Mail" (if they still them "Tree Mails").
I had forgotten that we give Dave our home email addresses!