can I put a music file in that will start playing when mail is opened

See this: http://forums.mozillazine.org/viewtopic.php?f=39&t=79970&start=0 I have to say that I'm not confident that using the html shown there would successfully attach the music file itself. It would probably play if the sender posted it to himself and opened it on his own computer, since the file is local (always assuming that his mail client permitted the playing.) Note that Thunderbird in particular won't play music embedded in messages, so if anyone you send to is using Thunderbird, they won't hear it. This is one reason why I use Thunderbird. Apart from always having the sound muted. It can be very embarrassing to have noise suddenly pop out of your computer in the workplace.