Is there any good way to launch UWP mail app through MAPISendMail function with file attachments from desktop app?
mailto: protocol will launch but it doesn’t attach files…

Update 2022-12-06:

To access Windows Runtime API from .NET Framework app, check: Call Windows Runtime APIs in desktop apps – Windows apps | Microsoft Learn

Edit csproj and add <TargetPlatformVersion>8.0</TargetPlatformVersion>

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <TargetPlatformVersion>8.0</TargetPlatformVersion>
  </PropertyGroup>
</Project>

And also add Windows reference. HintPath is mandatory and its important file Windows.winmd is included in Windows 10 SDK.

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <ItemGroup>
    <Reference Include="Windows">
      <HintPath>C:Program Files (x86)Windows Kits10UnionMetadata10.0.19041.0Windows.winmd</HintPath>
    </Reference>
    <Reference Include="System.Runtime.WindowsRuntime" />
  </ItemGroup>

</Project>

And code:

namespace ConsoleApp76
{
    internal class Program
    {
        static void Main(string[] args)
        {
            var file = StorageFile.GetFileFromPathAsync(@"C:filepath").AsTask().Result;
            Console.WriteLine(SharedStorageAccessManager.AddFile(file));
        }
    }
}

A sharing token will be retrieved in string.

7808B122-02DD-4996-A22D-C1D9EEC880E4