You can't use sound encoded in mp3, AAC or ogg vorbis in Windows Mail and Outlook Express, for example. Windows Live Mail does support mp3 files.
Formats Supported for Background Sound in Windows Live Mail
Music file formats you can use for background sound in Windows Live Mail:
- .wav, .au, .aif, .aifc, .aiff and .snd wave files
- .mid, .mi and .midi MIDI files
- .wma Windows Media Audio files
- .mp3 audio files
Formats Supported for Background Sound in Windows Mail and Outlook Express
Here's the list of what is supported for background sound in Windows Mail and Outlook Express:
- .wav, .au, .aif, and .snd wave files
- .mid and .rmi MIDI files
- .ra, .rm, .ram and .rmm Real Media files
