How to check that outgoing Outlook Mail Item is with digital signature or encrypted from VSTO Add-in in C#?

How to capture whether user has checked to send Outlook Mail with digital signature or encrypted from VSTO Add-in in C# ?

We can use the following code snippet with VSTO SE Outlook Skeleton project to build sample add-in:

IMPORTANT NOTE: This add-in will only work if we are NOT using Word as default email editor.

/*NOTE: Following programming examples is for illustration only, without warranty either expressed or implied,  
including, but not limited to, the implied warranties of merchantability and/or fitness for a particular purpose.   
This sample code assumes that you are familiar with the programming language being demonstrated and the tools used
to create and debug procedures.*/

    1:  using System;

    2:  using System.Windows.Forms;

    3:  using Microsoft.VisualStudio.Tools.Applications.Runtime;

    4:  using Outlook = Microsoft.Office.Interop.Outlook;

    5:  using Office = Microsoft.Office.Core;

    6:   

    7:  namespace OutlookAddin1

    8:  {

    9:      public partial class ThisApplication

   10:      {

   11:          private void ThisApplication_Startup(object sender, System.EventArgs e)

   12:          {

   13:              this.ItemSend +=new Microsoft.Office.Interop.Outlook.ApplicationEvents_11_ItemSendEventHandler(ThisApplication_ItemSend);   

   14:          }

   15:   

   16:          private void ThisApplication_Shutdown(object sender, System.EventArgs e)

   17:          {

   18:          }

   19:          private Office.CommandBarButton EncButton = null;

   20:          private Office.CommandBarButton DigButton = null;

   21:          private void ThisApplication_ItemSend(object Item, ref bool Cancel)

   22:          {

   23:              Outlook.MailItem mItem = null;

   24:    

   25:              try

   26:              {

   27:                  mItem = Item as Outlook.MailItem;

   28:   

   29:                  EncButton = (Office.CommandBarButton) mItem.GetInspector.CommandBars.FindControl(Office.MsoControlType.msoControlButton , 718, Type.Missing, true);

   30:                  if (EncButton.State ==  Office.MsoButtonState.msoButtonDown )

   31:                  {

   32:                      MessageBox.Show ("Mail will be Encrypted");

   33:                  }

   34:   

   35:                  DigButton = (Office.CommandBarButton)mItem.GetInspector.CommandBars.FindControl(Office.MsoControlType.msoControlButton, 719, Type.Missing, true);

   36:                  if (DigButton.State == Office.MsoButtonState.msoButtonDown)

   37:                  {

   38:                      MessageBox.Show ("Mail will be Digitally signed");

   39:                  }

   40:                  

   41:              }

   42:              catch (Exception ex)

   43:              {

   44:                  System.Windows.Forms.MessageBox.Show(ex.Message);

   45:                  Cancel = true;

   46:              }

   47:   

   48:          }

   49:          #region VSTO generated code

   50:   

   51:          /// <summary>

   52:          /// Required method for Designer support - do not modify

   53:          /// the contents of this method with the code editor.

   54:          /// </summary>

   55:          private void InternalStartup()

   56:          {

   57:              this.Startup += new System.EventHandler(ThisApplication_Startup);

   58:              this.Shutdown += new System.EventHandler(ThisApplication_Shutdown);

   59:          }

   60:   

   61:          #endregion

   62:      }

   63:  }

Please refer to following article related to working with CommandBars in Outlook Solution:

How to Use CommandBars in Outlook Solutions
https://support.microsoft.com/kb/201095

The above article also have a Microsoft Excel Macro to generate a list of Outlook 2000/2003 CommandBar control IDs.