Can I read an Outlook (2003/2007) PST file in C#?

As already mentioned in one of your linked SO questions, I'd also recommend using the Redemption library. I'm using it in a commercial application for processing Outlook mails and performing various tasks with them. It's working flawlessly and prevents showing up the annoying security alerts. It would mean using COM Interop, but that shouldn't be a problem.

There's a library in that package called RDO which is replacing the CDO 1.21, which lets you access PST files directly. Then it's as easy as writing (VB6 code):

set Session = CreateObject("Redemption.RDOSession")
'open or create a PST store
set Store = Session.LogonPstStore("c:\temp\test.pst")
set Inbox = Store.GetDefaultFolder(6) 'olFolderInbox
MsgBox Inbox.Items.Count

I went through and did the refactoring for subfolders

    private static IEnumerable<MailItem> readPst(string pstFilePath, string pstName)
    {
        List<MailItem> mailItems = new List<MailItem>();
        Microsoft.Office.Interop.Outlook.Application app = new Microsoft.Office.Interop.Outlook.Application();
        NameSpace outlookNs = app.GetNamespace("MAPI");

        // Add PST file (Outlook Data File) to Default Profile
        outlookNs.AddStore(pstFilePath);

        string storeInfo = null;

        foreach (Store store in outlookNs.Stores)
        {
            storeInfo = store.DisplayName;
            storeInfo = store.FilePath;
            storeInfo = store.StoreID;
        }

        MAPIFolder rootFolder = outlookNs.Stores[pstName].GetRootFolder();

        // Traverse through all folders in the PST file
        Folders subFolders = rootFolder.Folders;

        foreach (Folder folder in subFolders)
        {
            ExtractItems(mailItems, folder);
        }
        // Remove PST file from Default Profile
        outlookNs.RemoveStore(rootFolder);
        return mailItems;
    }

    private static void ExtractItems(List<MailItem> mailItems, Folder folder)
    {
        Items items = folder.Items;

        int itemcount = items.Count;

        foreach (object item in items)
        {
            if (item is MailItem)
            {
                MailItem mailItem = item as MailItem;
                mailItems.Add(mailItem);
            }
        }

        foreach (Folder subfolder in folder.Folders)
        {
            ExtractItems(mailItems, subfolder);
        }
    }

The Outlook Interop library is not just for addins. For example it could be used to write a console app that just reads all your Outlook Contacts. I am pretty sure that the standard Microsoft Outlook Interop library will let you read the mail - albeit it will probably throw a security prompt in Outlook that the user will have to click through.

EDITS: Actually implementing mail reading using Outlook Interop depends on what your definition of 'standalone' means. The Outlook Interop lib requires Outlook to be installed on the client machine in order to function.

// Dumps all email in Outlook to console window.
// Prompts user with warning that an application is attempting to read Outlook data.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Outlook = Microsoft.Office.Interop.Outlook;

namespace OutlookEmail
{
class Program
{
    static void Main(string[] args)
    {
        Outlook.Application app = new Outlook.Application();
        Outlook.NameSpace outlookNs = app.GetNamespace("MAPI");
        Outlook.MAPIFolder emailFolder = outlookNs.GetDefaultFolder(Microsoft.Office.Interop.Outlook.OlDefaultFolders.olFolderInbox);

        foreach (Outlook.MailItem item in emailFolder.Items)
        {
            Console.WriteLine(item.SenderEmailAddress + " " + item.Subject + "\n" + item.Body);
        }
        Console.ReadKey();
    }
}
}