pinvoke.net: Edit: mapi32.MAPISendMail

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Summary: MAPISendMail - Sends a message.

!!!!C# Signature:
  /// <summary>
  /// The MAPISendMail function sends a message.
  /// 
  /// This function differs from the MAPISendDocuments function in that it allows greater 
  /// flexibility in message generation.
  /// </summary>
  [DllImport("MAPI32.DLL", CharSet=CharSet.Ansi)]
  public static extern uint MAPISendMail(IntPtr lhSession, IntPtr ulUIParam, 
    MapiMessage lpMessage, uint flFlags, uint ulReserved);
!!!!VB Signature:
    <DllImport("MAPI32.DLL")> _
    Private Shared Function MAPISendMail(ByVal sess As IntPtr, ByVal hwnd As IntPtr, ByVal message As MapiMessage, 
       ByVal flg As Integer, ByVal rsv As Integer) As Integer
        End Function

!!!!User-Defined Structures:
[MAPI]
!!!!User-Defined Constants:
[MAPI]
!!!!Notes:
This signature is valid, if the MapiMessage is defined as a class. If MapiMessage is defined as a structure a 'ref' has to be added before 'MapiMessage lpMessage' parameter

!!!!Tips & Tricks:
Watch it! MAPI32 is not supported from managed code [http://blogs.msdn.com/mstehle/archive/2007/10/03/fyi-why-are-mapi-and-cdo-1-21-not-supported-in-managed-net-code.aspx]
Please add some!
!!!!Sample Code:
        [DllImport("MAPI32.DLL")]
        static extern int MAPISendMail(IntPtr sess, IntPtr hwnd, MapiMessage message, int flg, int rsv);

public int SendMail(string fileName)
        {
            MapiMessage msg = new MapiMessage();
            msg.subject = "Hello World!";
            msg.noteText = "See attached file for details";
            msg.files = GetAttachments(fileName, out msg.fileCount);

int result = MAPISendMail(new IntPtr(0), new IntPtr(0), msg, 0x00000001 | 0x00000008, 0);
            if (result > 1 || result < 0)
                throw new System.InvalidOperationException();
            return result;
        }

IntPtr GetAttachments(string fileName, out int fileCount)
        {
            int size = Marshal.SizeOf(typeof(MapiFileDesc));
            IntPtr intPtr = Marshal.AllocHGlobal(size);

MapiFileDesc mapiFileDesc = new MapiFileDesc();
            //An integer used to indicate where in the message text to render the attachment. 
            mapiFileDesc.position = -1;
            int ptr = (int)intPtr;
            
            mapiFileDesc.name = Path.GetFileName(fileName);
            mapiFileDesc.path = fileName;
            Marshal.StructureToPtr(mapiFileDesc, (IntPtr)ptr, false);
            ptr += size;

fileCount = 1;
            return intPtr;
        }
    }

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public class MapiMessage
    {
        public int reserved;
        public string subject;
        public string noteText;
        public string messageType;
        public string dateReceived;
        public string conversationID;
        public int flags;
        public IntPtr originator;
        public int recipCount;
        public IntPtr recips;
        public int fileCount;
        public IntPtr files;
    }

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public class MapiFileDesc
    {
        public int reserved;
        public int flags;
        public int position;
        public string path;
        public string name;
        public IntPtr type;
    }
!!!!Alternative Managed API:
Do you know one?  Please contribute it!

Documentation: MAPISendMail@msdn on MSDN