The best way is to use the Outlook classes or API. You should be able to access the attachment as HTML but the details are specific to Outlook. If you want to do that then you need to ask about Outlook. There is not a general-purpose solution for all email clients. Note that you did not specify in your original message that you need to do this for an Outlook message.

I am assuming that you have read my article, especially the part about HtmlDocument and HTMLDocument.

First add a reference to "Microsoft HTML Object Library"; it is a COM Object, not in the .Net library. Then the following console program shows how to get HTML into an HTML document.

using System;



namespace _97922

{

	class Program

	{

		const String htmltext = "
Header
Document text.
";

		static void Main(string[] args)

		{

			mshtml.IHTMLDocument2 Document = new mshtml.HTMLDocumentClass();

			Document.write(new object[] { htmltext });

			Document.close();

			mshtml.IHTMLElementCollection Elements = Document.body.children as mshtml.IHTMLElementCollection;

			if (Elements == null)

			{

				Console.WriteLine("No elements");

				return;

			}

			mshtml.IHTMLElement e = null;

			for (int i = 0; i < Elements.length; ++i)

			{

				e = Elements.item(i) as mshtml.IHTMLElement;

				if (e == null)

					Console.WriteLine("Unknown object at {0}", i);

				else

					Console.WriteLine(e.tagName);

			}

		}

	}

}