Extracting/Scanning emails from Outlook using C#

I'm trying to make a windows form application that can be "hidden" in the taskbar (like WiFi and so on), equipped with a timer, and that every 10 seconds it scans my email inbox in Outlook.

The first part works fine, but I can't get the scan to work. At first i just want to extract the names of email subjects and put them into a text file, just to test the code. But in the end i'd like to scan one particular inbox (i have several on my outlook, like 5 or 6, with different mail address associeted, and i can't find anything on the internet to target one of them) and make a popup or something when particular email are received.

Anyway, this is the code i have so far:

    public static bool isRunning = false;

    public Form1()
    {
        InitializeComponent();

        System.Timers.Timer timer = new System.Timers.Timer(10000);
        timer.Elapsed += OnTimedEvent;
        timer.Enabled = true;
    }


    private void Hide_Click(object sender, EventArgs e)
    {
        this.Hide();
        notifyIcon1.Visible = true;
    }

    private void notifyIcon1_MouseClick(object sender, MouseEventArgs e)
    {
        this.Show();
        notifyIcon1.Visible = false;
    }

    private static void OnTimedEvent(object source, ElapsedEventArgs e)
    {
        Outlook.Application app = null;
        Outlook.MAPIFolder inbox = null;
        Outlook._NameSpace ns = null;

        if (Process.GetProcessesByName("OUTLOOK").Count() > 0)
        {
            try
            {
                app = Marshal.GetActiveObject("Outlook.Application") as Outlook.Application;
                inbox = ns.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderInbox);
                ns = app.GetNamespace("MAPI");
                List<Outlook.MailItem> ReceivedEmail = new List<Outlook.MailItem>();
                List<string> titles = new List<string>();

                foreach (Outlook.MailItem mail in inbox.Items)
                {
                    ReceivedEmail.Add(mail);
                }

                foreach (Outlook.MailItem mail in ReceivedEmail)
                {
                    titles.Add(mail.Subject.ToString());
                }

                File.WriteAllLines("C://Users/A222946/Desktop/allMails.txt", titles);

            }
            catch (System.Runtime.InteropServices.COMException ex)
            {
                MessageBox.Show(ex.Message);
            }
            catch (System.Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        else
        {
            MessageBox.Show("Please, start outlook..");
        }

    }
}

The error i find when i'm running this is the following:

Operation unavailable (Exception from HRESULT: 0x800401E3 (MK_E_UNAVAILABLE)

I tried with and without administrator rights, same error.

Update

So after some changes it looks like this now:

private static void OnTimedEvent(object source, ElapsedEventArgs e)
    {
        Outlook.Application app = new Outlook.Application();
        Outlook.MAPIFolder inbox = null;
        Outlook._NameSpace ns = null;
        Outlook.Items items = null;

        if (Process.GetProcessesByName("OUTLOOK").Count() > 0)
        {
            try
            {
                app = Marshal.GetActiveObject("Outlook.Application") as Outlook.Application;
                ns = app.GetNamespace("MAPI");
                inbox = ns.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderInbox);
                items = inbox.Items;
                List<Outlook.MailItem> ReceivedEmail = new List<Outlook.MailItem>();
                List<string> titles = new List<string>();

                foreach (Object obj in items)
                {
                    if (obj is Outlook.MailItem)
                    {
                        ReceivedEmail.Add((Outlook.MailItem)obj);
                    } 
                }

                foreach (Outlook.MailItem mail in ReceivedEmail)
                {
                    titles.Add(mail.Subject.ToString());
                }

                File.WriteAllLines("C://Users/A222946/Desktop/allMails.txt", titles);

            }
            catch (COMException ex)
            {
                MessageBox.Show(ex.Message);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        else
        {
            MessageBox.Show("Please, start outlook..");
        }

    }

But i still have this error:

object reference not set to an instance of an object

Also, do you have any idea how i could target one particular mailbox? Example: "abcdefg@blabla.com"

I think the COM components are not accessible. COM components are used by some of the Windows components(like MS Office).You need to make use of STAThreadAttribute.

[STAThread]
static void Main(string[] args)
{
    // etc..
}

I think this should fix the issue.