Avoid or remove lock from StgOpenStorage()

Question

Greets,

I try to open an outlook .msg file with StgOpenStorage().

My problem is, that StgOpenStorage always locks my file. So, how can I avoid/remove the lock StgOpenStorage() adds to my file?
(see last method of code OpenStorage())

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;

namespace IStorageLock
{
	[ComImport]
	[Guid("0000000d-0000-0000-C000-000000000046")]
	[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
	public interface IEnumSTATSTG
	{
		// The user needs to allocate an STATSTG array whose size is celt.
		[PreserveSig]
		uint Next(uint celt,
		          [MarshalAs(UnmanagedType.LPArray), Out]
		          System.Runtime.InteropServices.ComTypes.STATSTG[] rgelt,
		          out uint pceltFetched);

		void Skip(uint celt);

		void Reset();

		[return: MarshalAs(UnmanagedType.Interface)]
		IEnumSTATSTG Clone();
	}

	[ComImport]
	[Guid("0000000b-0000-0000-C000-000000000046")]
	[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
	interface IStorage
	{
		void CreateStream(string pwcsName, uint grfMode, uint reserved1,
		                  uint reserved2, out IStream ppstm);

		void OpenStream(string pwcsName, IntPtr reserved1, uint grfMode,
		                uint reserved2, out IStream ppstm);

		void CreateStorage(string pwcsName, uint grfMode, uint reserved1,
		                   uint reserved2, out IStorage ppstg);

		void OpenStorage(string pwcsName, IStorage pstgPriority, uint grfMode,
		                 IntPtr snbExclude, uint reserved, out IStorage ppstg);		

		void CopyTo(uint ciidExclude, Guid rgiidExclude, IntPtr snbExclude,
		            IStorage pstgDest);

		void MoveElementTo(string pwcsName, IStorage pstgDest,
		                   string pwcsNewName, uint grfFlags);

		void Commit(uint grfCommitFlags);

		void Revert();

		void EnumElements(uint reserved1, IntPtr reserved2, uint reserved3,
		                  out IEnumSTATSTG ppenum);

		void DestroyElement(string pwcsName);

		void RenameElement(string pwcsOldName, string pwcsNewName);

		void SetElementTimes(string pwcsName,
		                     System.Runtime.InteropServices.ComTypes.FILETIME pctime,
		                     System.Runtime.InteropServices.ComTypes.FILETIME patime,
		                     System.Runtime.InteropServices.ComTypes.FILETIME pmtime);		

		void SetClass(Guid clsid);

		void SetStateBits(uint grfStateBits, uint grfMask);

		void Stat(out System.Runtime.InteropServices.ComTypes.STATSTG pstatstg,
		          uint grfStatFlag);
	}

	class Lock
	{
		[Flags]
		public enum STGM : int {
			DIRECT           = 0x00000000,
			TRANSACTED       = 0x00010000,
			SIMPLE           = 0x08000000,
			READ             = 0x00000000,
			WRITE            = 0x00000001,
			READWRITE        = 0x00000002,
			SHARE_DENY_NONE  = 0x00000040,
			SHARE_DENY_READ  = 0x00000030,
			SHARE_DENY_WRITE = 0x00000020,
			SHARE_EXCLUSIVE  = 0x00000010,
			PRIORITY         = 0x00040000,
			DELETEONRELEASE  = 0x04000000,
			NOSCRATCH        = 0x00100000,
			CREATE           = 0x00001000,
			CONVERT          = 0x00020000,
			FAILIFTHERE      = 0x00000000,
			NOSNAPSHOT       = 0x00200000,
			DIRECT_SWMR      = 0x00400000,
		}

		[DllImport("ole32.dll")]
		private static extern int StgIsStorageFile([MarshalAs(UnmanagedType.LPWStr)]
		                                           string pwcsName);

		[DllImport("ole32.dll")]
		static extern int StgOpenStorage([MarshalAs(UnmanagedType.LPWStr)]
		                                 string       pwcsName,
		                                 IStorage     pstgPriority,
		                                 STGM         grfMode,
		                                 IntPtr       snbExclude,
		                                 uint         reserved,
		                                 out IStorage ppstgOpen);

		public IStorage OpenStorage(string fileName)
		{
			if (StgIsStorageFile(fileName) != 0) {
				return null;
			}

			IStorage storage = null;

			//
			// StgOpenStorage() locks file 'fileName'
			//
			// Set flags like:
			// [http://stackoverflow.com/questions/1086814/opening-ole-compound-documents-read-only-with-stgopenstorage]
			//
			int stgOpenStorage = StgOpenStorage(fileName, null,
			                                    STGM.READ            |
			                                    STGM.SHARE_DENY_NONE |
			                                    STGM.TRANSACTED,
			                                    IntPtr.Zero, 0,
			                                    out storage);
			//
			// Try to rename file (for testing purposes only)
			//
			try {
				File.Move(fileName, fileName + @".renamed");
			} catch (Exception ex) {		// exception: file alreay in use by another process
				throw;
			}

			if (stgOpenStorage != 0) {
				return null;
			} else {
				return storage;
			}
		}
	}
}

Regards,

inno