C#: add a resource as an attachment to an Outlook mail item

I'm trying to attach a file to an email that will be sent in Outlook, in C#.
I've got the following that works great:

using OutlookApp = Microsoft.Office.Interop.Outlook.Application;
[...]
public class Foo
{
    private void SendMail()
    {
        OutlookApp outlookApp = new OutlookApp();
        MailItem mailItem = outlookApp.CreateItem(OlItemType.olMailItem);
        [...]
        var rootDirectory = System.Windows.Forms.Application.StartupPath;
        Attachment myAttachment = mailItem.Attachments.Add(Path.Combine(rootDirectory, @"../../Assets/image.png"));
        [...]
        mailItem.Display(false);
    }
}

It works, but it sucks a bit because right now my file is in a static folder that won't be there when the project is built.
So I've put my image in the resources of the project: the image is now available via Properties.Resources.image.
Naively, I've done the following:

using OutlookApp = Microsoft.Office.Interop.Outlook.Application;
[...]
public class Foo
{
    private void SendMail()
    {
        OutlookApp outlookApp = new OutlookApp();
        MailItem mailItem = outlookApp.CreateItem(OlItemType.olMailItem);
        [...]
        var rootDirectory = System.Windows.Forms.Application.StartupPath;
        Attachment myAttachment = mailItem.Attachments.Add(Properties.Resources.image);
        [...]
        mailItem.Display(false);
    }
}

But it doesn't work:

System.Runtime.InteropServices.COMException: 'Member not found. (Exception from HRESULT: 0x80020003 (DISP_E_MEMBERNOTFOUND))'

From MSDN, I read for the first parameter of the Attachments.Add method that:

Type: System.Object
The source of the attachment. This can be a file (represented by the full file system path with a file name) or an Outlook item that constitutes the attachment.

The problem, as I understand it, is that I can only provide a file name in order to add an attachment to an Outlook mail. The other option would be to create an Outlook attachment, but if I understand it's not possible. The only way of doing that is by... Adding a file the the attachments of the mailItem.
So my questions are the following:

1. is my approach correct to add an attachment? If so, how can I do to get the path of the resource file?
2. if this approach is a good one, is there a way to reference a file elsewhere than the Resources.resx file in the projet? Meaning: the file path will be available in my application and the file will be "exported" when I build the project;
3. if my approach is not correct, how can I add an attachment to a MailItem from a resource file properly?

Thanks.

OK, in the end I adapted my method. In the build action for all the images that I needed, I did the following (this is available in the property tab for the file):

• Build action: Content.
• Copy to output directory: Copy if newer.

That way, at build, the folder containing my images (and my images) are copied to the build directory. I can then use their relative URL:

Attachment myAttachment = mailItem.Attachments.Add(Path.GetFullPath("Assets/image.png"));

I don't know if it's the only way to do it, but it works, it doesn't seem ugly and I can still use the images in the XAML. When images are placed in a resx file, apparently, it's a PITA.