EWB client code:

procedure TLoginForm.Button1Click(Sender: TObject);
begin
  with PostRequest do
  begin
    Params.clear;
    URL := 'modules/sendmail';
    RequestContent.text := 'Lorem ipsum dolor sit amet...';
    RequestHeaders.Values['Content-Type'] := 'plain/text';
    RequestHeaders.Values['Content-Length']:=IntToStr(Length(RequestContent.Text));
    Params.add('method=mail');
    Execute;
  end;
end;

procedure TLoginForm.PostRequestComplete(Request: TServerRequest);
begin
  showmessage(IntToStr(Request.StatusCode));
end; 

EWB module code:

procedure TSendMailModule.EWBModuleExecute(Request: TEWBServerRequest);
var
  TempStrings: TStrings;
  slLog: TStringList;
begin

  slLog := TStringList.Create;
  try
    slLog.Add('Request received');
    slLog.SaveToFile('c:\test.log');
  finally
    slLog.Free;
  end;
  Request.SendError(200, '');
end;