[Alexandro]

Hola a todos y gracias por responder. He encontrado esto:

Código Delphi [-]
function NetSend(dest, source, msg: string): longint;
type
 TNetMessageBufferSendFunction = function(servername, msgname, fromname: PWideChar; buf:
 PWideChar; buflen: Cardinal): longint; stdcall;
var
 NetMessageBufferSend: TNetMessageBufferSendFunction;

 SourceWideChar  : PWideChar;
 DestWideChar   : PWideChar;
 MessagetextWideChar: PWideChar;

 Handle      : THandle;
begin

 Handle := LoadLibrary('NETAPI32.DLL');
 if Handle = 0 then
 begin
 Result := GetLastError;
 exit;
 end;
 @NetMessageBufferSend := GetProcAddress(Handle, 'NetMessageBufferSend');
 if @NetMessageBufferSend = nil then
 begin
 Result := GetLastError;
 exit;
 end;
 MessagetextWideChar := nil;
 try
 GetMem(MessagetextWideChar, Length(msg) * SizeOf(WideChar) + 1);
 GetMem(DestWideChar, 20 * SizeOf(WideChar) + 1);
 StringToWideChar(msg, MessagetextWideChar, Length(msg) * SizeOf(WideChar) + 1);
 StringToWideChar(Dest, DestWideChar, 20 * SizeOf(WideChar) + 1);
 if source = '' then
 begin
  result := NetMessageBufferSend(nil, DestWideChar, nil, MessagetextWideChar, Length(msg) * SizeOf(WideChar) + 1)
 end else
 begin
  GetMem(SourceWideChar, 20 * SizeOf(WideChar) + 1);
  StringToWideChar(source, SourceWideChar, 20 * SizeOf(WideChar) + 1);
  result := NetMessageBufferSend(nil, DestWideChar, SourceWideChar, MessagetextWideChar,
       Length(msg) * SizeOf(WideChar) + 1);
  freemem(SourceWideChar);
 end;
 finally
 FreeMem(MessagetextWideChar);
 FreeLibrary(Handle);
 end;
end;

Voy a probar. Les comento luego...