Opening the default e-email app

Question

Hello everyone and happy new year. As you can see, I have a list of files in a listview and a share button. The problem is that I want to open the e-mail client you have by default.

I tried this code, but it gives me an error

string mailAppPath;
using (var key = Registry.ClassesRoot.OpenSubKey("mailto")) {
    mailAppPath = key?.GetValue("").ToString();
}
if (!string.IsNullOrEmpty(mailAppPath)) {
    // Use the mailAppPath variable to start the process
    Process p = new();
    p.StartInfo.FileName = mailAppPath;
    p.Start();
}

System.ComponentModel.Win32Exception: 'An error occurred trying to start process 'URL:MailTo Protocol' with working directory 'the directory that I am working on'. The system cannot find the file specified.'

I guess that for some reason is trying to look in my project directory, specifically the BIN/Windows10 bla bla

Answer 1

I want to open the e-mail client you have by default

Usually, it could be done with mailto: protocol in FileName, like "mailto:test@test.com?subject=Subject&body=Body",

but it does not work anymore on my PC (Windows 10)

Other methods are with MAPI

This test works for me with a "E:\test.docx" file as attachment (add a Button for the test on the Click) :

    public partial class Form1 : Form
    {
        public enum HRESULT : int
        {
            S_OK = 0,
            S_FALSE = 1,
            E_NOINTERFACE = unchecked((int)0x80004002),
            E_NOTIMPL = unchecked((int)0x80004001),
            E_FAIL = unchecked((int)0x80004005),
        }

        [ComImport]
        [Guid("00000122-0000-0000-C000-000000000046")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        public interface IDropTarget
        {
            HRESULT DragEnter(
                [In] System.Runtime.InteropServices.ComTypes.IDataObject pDataObj,
                [In] int grfKeyState,
                [In] Point pt,
                [In, Out] ref int pdwEffect);

            HRESULT DragOver(
                [In] int grfKeyState,
                [In] Point pt,
                [In, Out] ref int pdwEffect);

            HRESULT DragLeave();

            HRESULT Drop(
                [In] System.Runtime.InteropServices.ComTypes.IDataObject pDataObj,
                [In] int grfKeyState,
                [In] Point pt,
                [In, Out] ref int pdwEffect);
        }

        public const int DROPEFFECT_NONE = (0);

        [DllImport("Shell32.dll", CharSet = CharSet.Unicode, SetLastError = true, EntryPoint = "#740")]
        public static extern HRESULT SHCreateFileDataObject(IntPtr pidlFolder, uint cidl, IntPtr[] apidl, System.Runtime.InteropServices.ComTypes.IDataObject pdtInner, out System.Runtime.InteropServices.ComTypes.IDataObject ppdtobj);

        [DllImport("Shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern HRESULT SHILCreateFromPath([MarshalAs(UnmanagedType.LPWStr)] string pszPath, out IntPtr ppIdl, ref uint rgflnOut);
  
        [DllImport("Shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern IntPtr ILFindLastID(IntPtr pidl);

        [DllImport("Shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern IntPtr ILClone(IntPtr pidl);

        [DllImport("Shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern Boolean ILRemoveLastID(IntPtr pidl);

        [DllImport("Shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern void ILFree(IntPtr pidl);
  
        Guid CLSID_MapiMail = new Guid("9E56BE60-C50F-11CF-9A2C-00A0C90A90CE");

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            HRESULT hr = HRESULT.E_FAIL;
            uint rgflnOut = 0;
            System.Runtime.InteropServices.ComTypes.IDataObject pDataObject;
            IntPtr pidlParent = IntPtr.Zero, pidlFull = IntPtr.Zero, pidlItem = IntPtr.Zero;
            var aPidl = new IntPtr[255];

            hr = SHILCreateFromPath("E:\\test.docx", out pidlFull, ref rgflnOut);
            if (hr == HRESULT.S_OK)
            {
                pidlItem = ILFindLastID(pidlFull);
                aPidl[0] = ILClone(pidlItem);
                ILRemoveLastID(pidlFull);
                pidlParent = ILClone(pidlFull);
                ILFree(pidlFull);

                hr = SHCreateFileDataObject(pidlParent, 1, aPidl, null, out pDataObject);
                if (hr == HRESULT.S_OK)
                { 
                    Type DropTargetType = Type.GetTypeFromCLSID(CLSID_MapiMail, true);
                    object DropTarget = Activator.CreateInstance(DropTargetType);
                    IDropTarget pDropTarget = (IDropTarget)DropTarget;
                    int pdwEffect = DROPEFFECT_NONE;
                    Point pt = new Point();
                    pt.X = 0;
                    pt.Y = 0;
                    hr = pDropTarget.Drop(pDataObject, 0, pt, pdwEffect);
                }

                if (pidlParent != IntPtr.Zero)
                    ILFree(pidlParent);
                if (aPidl[0] != IntPtr.Zero)
                    ILFree(aPidl[0]);
            }
        }
    }