'Utils is a Class, but in your code you never create an
instance of that class.
Like this: Utils currentUtils = new Utils();
Once you have an instance of the Class, you can access the Public List<string>stringList
Like this (in your Main Form):
foreach(string receivableItem in currentUtils.stringList)
{
listBox.Items.Add(receivableItem);
}
Note: your EventHandler has no access modifier, and, so, is, by default, private access: unless you make it 'public, or 'internal, no object outside Utils can use/subscribe to it. So, what you show is not working code.