I get zero 0 byte attachments on the following email clients...

Yahoo! Mail via web browser
Hotmail (Windows Live) mail via web browser

and do not have any problem with Gmail via web browser. So the simple fix is to use Gmail but it would be nice to get Yahoo and Hotmail working. I'm guessing this might be a way the email is attached or how Yahoo and MS are handing the email attached WAV file on their end?