Using tbxEmailAddress to display Last Name, First Name in a listbox

string lastname = txtEmailAddress.Text.Substring(0, txtEmailAddress.Text.IndexOf("."));
string firstname = txtEmailAddress.Text.Substring(txtEmailAddress.Text.IndexOf(".") + 1, txtEmailAddress.Text.IndexOf('@') - lastname.Length - 1);

listBox1.Items.Add(lastname + ", " + firstname);