The forum default is to show the last month of activity. In the forum section, there is a menu at the bottom to change the display options if you want to see threads with posts prior to that. If you don't like the default, you can customize the Default Age Cutoff in the Edit Options section of the user Control Panel.
On the email that Kingmobileaudio is receiving, they can go into the Control Panel and edit their subscriptions (I'm guessing that they may be subscribed to the Nebraska section and any new activity or thread will kick out an email), or go into Edit Options and just turn off email notifications for subscribed threads.