sending html file

Try using the phpmailer class

then use the docs to send the mail, you can attach files..., etc, smtp authentication, etc.. :D
Ah, tranquillo, this thread is over two months old and the poster hasn't made a post since February 2. I don't think he's coming back.
tranquillo, as you don´t want to send it as an attachment, you can make some routine to open the fine, copy its html content and send it as/with your HTML Mail!