Adobe Flex - Open the email client with attachment

I'm developing an application in flex and I need to open an email client (for example: gmail app) with the bcc, subject, body and an attach file. I use the mailto but it seems that the attch file doesn't work... This is the code that I am working:

navigateToURL(new URLRequest("mailto:xpto@gmail.com?subject=SomeText&body=OtherSomeText&Attachment=C:\Users\XPTO\abc.txt")));

Can I do this with mailto or there is another way to do this?