You can use MailBrowserControl control. Add reference to all three assemblies: Mail.dll, MailBrowserControl.dll, ProtocolEx.dll.
MailBrowserControl is defined in Limilabs.Windows.
private void button1_Click(object sender, EventArgs e)
{
IMail mail = new MailBuilder().CreateFromEmlFile(@"HTMLMail.eml");
mailBrowser1.Navigate(new MailHtmlDataProvider(mail));
}
You can find details here:
https://www.limilabs.com/blog/display-html-email-in-windows-application