It could depend on the e-mail client software you are using.
To add background sounds or music to your emails in Windows Live Mail, Windows Mail or Outlook Express, you can do the following:
- Start writing a new message in HTML format.
- Select Format - Background - Sound... from the menu.
- Use the Browse button to locate and choose the sound file that you want to be played in the background.
- Specify whether you want the sound file to be played continuously or a certain number of times.
- Click OK.