E-mail with attachment wich you create in the form

I like to send an mail with an attachment.
But the attachmant is not an file, but in fact its a html mail wich i create in the body like the var mailbody.
I like to add the mailbody as attachment as a html file. So it can be attachment.html
How can i do that, because the easyest way to add an attachment to an e-mail is by adding a file...

Try

            dim mailbody as string = "<h1>This is a test</h1>";


            myMessage = New MailMessage()
            With myMessage
                .To = sendTo
                .From = From
         &nb ...