保存（保存为）数字签名邮件时，Outlook会向用户提示一个消息框问题“您即将以不安全的格式保存数字签名电子邮件。是否继续？"。
我需要Outlook在不显示消息框的情况下保存该消息。是否有任何方法可以通过Outlook设置、注册表项或编程方式抑制此消息？
另一个复杂的是，Outlook是通过服务执行.我可以成功地以编程方式响应消息框是各种方式，但没有一个工作时，作为一个服务运行. SendKeys，SendMessage，PostMessage和SendInput都工作时，在桌面上运行，但失败时，作为一个服务运行.

Process p = Process.GetProcessesByName("OUTLOOK").FirstOrDefault();
            if (p != null)
            {
                IntPtr h = p.MainWindowHandle;
                SetForegroundWindow(h);
                // SendKeys works when running on the desktop, but not when running as a service.
                SendKeys.SendWait("y");
                // SendMessage works when running on the desktop, but not when running as a service.
                SendMessage(h, WM_KEYDOWN, 0x59, 0);
                // PostMessage works when running on the desktop, but not when running as a service.
                PostMessage(h, WM_KEYDOWN, 0x59, 0);
                // SendInput works when running on the desktop, but not when running as a service.
                Input[] inputs = new Input[]
                {
                    new Input
                    {
                        type = (int)InputType.Keyboard,
                        u = new InputUnion
                        {
                            ki = new KeyboardInput
                            {
                                wVk = 0,
                                wScan = 0x15, // Y
                                dwFlags = (uint)(KeyEventF.KeyDown | KeyEventF.Scancode),
                                dwExtraInfo = GetMessageExtraInfo()
                            }
                        }
                    },
                    new Input
                    {
                        type = (int)InputType.Keyboard,
                        u = new InputUnion
                        {
                            ki = new KeyboardInput
                            {
                                wVk = 0,
                                wScan = 0x15, // Y
                                dwFlags = (uint)(KeyEventF.KeyUp | KeyEventF.Scancode),
                                dwExtraInfo = GetMessageExtraInfo()
                            }
                        }
                    }
                };
                SendInput((uint)inputs.Length, inputs, Marshal.SizeOf(typeof(Input)));
            }

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这是一种抑制或响应对话框的方法吗？Outlook加载项可以检测到对话框并将其关闭吗？