Reading outlook .msg files

I got thousand of msg files in a single folder. I would like to read msg files using c# to get the subject of those emails.
I first added a reference to the Microsoft Outlook 14.0 Object Library into the application, and then wrote the code below:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
using Outlook = Microsoft.Office.Interop.Outlook;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string[] files = Directory.GetFiles(@"C:\test", "*.msg", SearchOption.AllDirectories);
            for(int i=0; i < files.Length; i++)
            {
                try
                {
                    Microsoft.Office.Interop.Outlook.Application app = new Microsoft.Office.Interop.Outlook.Application();
                    var item = app.Session.OpenSharedItem(files[i]) as Outlook.MailItem;
                    textBox1.Text += item.Subject + Environment.NewLine;
                    item.Close(Outlook.OlInspectorClose.olDiscard);
                }
                catch (Exception)
                {   
                    //throw;
                }
            }
        }
    }
}

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Q1. When the application is running, Outlook tray icon will appear. Is there any other options/library able to access the msg files without showing the icon?

Q2. One warning in the error list after built the solution
"Ambiguity between method 'Microsoft.Office.Interop.Outlook._MailItem.Close(Microsoft.Office.Interop.Outlook.OlInspectorClose)' and non-method 'Microsoft.Office.Interop.Outlook.ItemEvents_10_Event.Close'. Using method group.".

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What is the difference between Microsoft.Office.Interop.Outlook._MailItem and Microsoft.Office.Interop.Outlook.MailItem? Which one should I use? Can I cast the item as Outlook._MailItem instead?

Q3. The program seems to use a lot of memory, how to release the object created by OpenSharedItem method properly?
bbkevinAsked:
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frankhelkCommented:
About Q1: I presume that instantiating objects from the Outlook classes (esp. the "app" object) is almost the same amount of activity than running Outlook itself ... it might even start some background processes to provide some of the services. I think that some component in that bundle activates its icon. I fear the only way to circumvent that would be to explore Outlook's msg file format (see i.e. HERE) and write your own, lean dissector. That would eleminate Q3 as well, I think ;-)
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Éric MoreauSenior .Net ConsultantCommented:
Aspose Email component can process msg files without even having Outlook installed: http://www.aspose.com/.net/email-component.aspx
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Alexei KuznetsovMicrosoft Outlook MVPCommented:
Q1: Creating an instance of Outlook.Application class includes running outproc server (outlook.exe). This is why you have Outlook tray icon. You can't change this behavior.

Q2: _MailItem is an interface while MailItem is a class that implements _MailItem. You can safely cast the object to _MailItem.

Q3: item.ReleaseComObject()

Advice1: Move Outlook.Application object creation and getting Session out of the "for" loop:
private void button1_Click(object sender, EventArgs e)
{
    var app = new Microsoft.Office.Interop.Outlook.Application();
    var session = app.Session;
    ...

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Use session.OpenSharedItem() inside the loop.

Advice2: Use textBox1.AppendText() method instead of "Text +=". This will significantly improve the performance on large number of items.
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