private void UpdateXml_List()
        {
            XmlDocument doc = new XmlDocument();
            doc.Load("C:\\windows\\temp\\mlst.xml");
            XmlElement root = doc.DocumentElement;
            XmlNodeList nodes = root.SelectNodes("//Mail");
            foreach (XmlNode node in nodes)
            {
                string date = node.InnerText;
                combo.Items.Add(date);
            }
        }

using System.IO;
using System.Xml;
namespace LinkSender
{
    public partial class Main : Form
    {
public Main()
        {
            CheckXml_File();
            LoadXml_List();
            InitializeComponent();
        }
private void LoadXml_List()
        {            
                XmlDocument doc = new XmlDocument();
                doc.Load("C:\\windows\\temp\\mlst.xml");
                foreach (XmlNode node in doc.SelectNodes("//Mail"))
                {
                    string mail = node.InnerText;
                    MailExp.Items.Add(mail);
                    MailTofes.Items.Add(mail);
                }             
        }

using System.IO;
using System.Xml;
namespace LinkSender
{
    public partial class Main : Form
    {
public Main()
        {
            CheckXml_File();           
            InitializeComponent();
        }
private void UpdateMail_List()
        {
            XmlDocument doc = new XmlDocument();
            doc.Load("C:\\WINDOWS\\Temp\\mlst.xml");
            XmlNode newElem;
            newElem = doc.CreateNode(XmlNodeType.Element, "Mail", "");
            newElem.InnerText = MailExp.Text;
            XmlElement root = doc.DocumentElement;
            root.AppendChild(newElem);
            try
            {
                doc.Save("C:\\WINDOWS\\Temp\\mlst.xml");
            }
            catch (Exception)
            {
                MessageBox.Show("Can't create Xml file!");
            }
            LoadXml_List(); (If I put it here it's doing the job.)
        }
private void LoadXml_List()
        {            
                XmlDocument doc = new XmlDocument();
                doc.Load("C:\\windows\\temp\\mlst.xml");
                foreach (XmlNode node in doc.SelectNodes("//Mail"))
                {
                    string mail = node.InnerText;
                    MailExp.Items.Add(mail);
                    MailTofes.Items.Add(mail);
                }             
        }