int email = txtUserEmail.Text.IndexOf("@");            
int spot = txtUserEmail.Text.LastIndexOf(".");
         if (email<0)            
            {
                MessageBox.Show("E-Mail格式不对，请重新输入！", "系统提示",MessageBoxButtons.OK,MessageBoxIcon.Information);
                txtUserEmail.Text = "";
                txtUserEmail.Focus();            
            }
         else if (spot < 0)            
            {
                MessageBox.Show("E-Mail格式不对，请重新输入！", "系统提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                txtUserEmail.Text = "";
                txtUserEmail.Focus();
            }