/// That is, attachments replace the character in the MapiMessage structure field

  /// A MapiMessage structure contains information about a message.

  public class MapiMessage {

    ''' A MapiMessage structure contains information about a message.

    Public Structure MapiMessage

    ''' That is, attachments replace the character in the MapiMessage structure field

    public class MapiMessage

    Public Class MapiMessage

    MapiMessage lpMessage, uint flFlags, uint ulReserved, string lpszMessageID);

    MapiMessage lpMessage, uint flFlags, uint ulReserved);

    Private Shared Function MAPISendMail(ByVal sess As IntPtr, ByVal hwnd As IntPtr, ByVal message As MapiMessage,

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

    static extern int MAPISendMail(IntPtr sess, IntPtr hwnd, MapiMessage message, int flg, int rsv);

        MapiMessage msg = new MapiMessage();

    public class MapiMessage

  /// MapiMessage structure.