C # P / Invoke. Маршал как char * __ptr32 в x64

Родная структура

struct MailBox
{
__time32_t time;            // receive time
int sender;                 // mail sender (login)
char from[64];              // mail sender (name)
int to;                     // mail recipient
char subject[128];          // mail sumbect
int readed;                 // readed flag
char* __ptr32 body;         // pointer to mail body
int bodylen;                // mail body length
short build_min;            // minimum build
short build_max;            // maximum build
int reserved;               // reserved
};

Структура в C #, которую я создал

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct NMailBox
{
internal UInt32 time;               // receive time
internal Int32 sender;              // mail sender (login)
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)]
internal string from;               // mail sender (name)
internal Int32 to;                  // mail recipient
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
internal string subject;            // mail sumbect
internal Int32 readed;              // readed flag
internal Int32 body;                // readed flag
internal Int32 bodylen;             // mail body length
internal short build_min;           // minimum build
internal short build_max;           // maximum build
internal Int32 reserved;            // reserved
}

Класс для доступа к структуре данных

public class MailBox : BaseModel<NMailBox>, IDisposable
{
/// <summary>
/// Receive time
/// </summary>
public DateTime Time
{
get { return native.time.ToDateTime(); }
set { native.time = value.ToUInt(); }
}

/// <summary>
/// Mail sender (login)
/// </summary>
public Int32 Sender
{
get { return native.sender; }
set { native.sender = value; }
}

/// <summary>
/// Mail sender (name)
/// </summary>
public string From
{
get { return native.from; }
set { native.from = value.CorrectString(64); }
}

/// <summary>
/// Mail recipient
/// </summary>
public Int32 To
{
get { return native.to; }
set { native.to = value; }
}

/// <summary>
/// Mail sumbect
/// </summary>
public string Subject
{
get { return native.subject; }
set { native.subject = value.CorrectString(128); }
}

/// <summary>
/// Readed flag
/// </summary>
public Int32 Readed
{
get { return native.readed; }
set { native.readed = value; }
}

public string Body
{
get
{
return Marshal.PtrToStringAnsi(native.body, native.bodylen);
}
set
{
if (native.body != IntPtr.Zero)
{
BodyFree();
if (native.body != IntPtr.Zero)
throw new Exception(nameof(native.body));
}

native.body = Marshal.StringToHGlobalAnsi(value);
native.bodylen = value.Length;
}
}

/// <summary>
/// Minimum build
/// </summary>
public short BuildMin
{
get { return native.build_min; }
set { native.build_min = value; }
}

/// <summary>
/// Maximum build
/// </summary>
public short BuildMax
{
get { return native.build_max; }
set { native.build_max = value; }
}

/// <summary>
/// Reserved
/// </summary>
public Int32 Reserved
{
get { return native.reserved; }
}

private void BodyFree()
{
if (native.body != IntPtr.Zero)
{
var pointer = native.body;
Marshal.FreeHGlobal(pointer);
native.bodylen = 0;
}
}

public void Dispose()
{
BodyFree();
}
}

Структура, используемая в нативных функциях с подписью

virtual int __stdcall MailSend(const MailBox* mail,const int *logins)=0;

Делегат, который я создал для него

[UnmanagedFunctionPointer(CallingConvention.StdCall)]
protected delegate ResultCode MailSendDelegate(IntPtr Obj, ref NMailBox mail, [In] int[] logins);

Проблема в том, что когда я вызываю наивную функцию и отправляю ей подготовленную структуру, я получаю
AccessViolationException

Подскажите, как исправить ошибку?