Does it matter whether 'single' or "double" quotes are used? I think you should be using single quotes, as per that PHP website.
Double quotes will interpolate variables inside the string, single will not.
to parameter needs spaces
http://uk.php.net/manual/en/function.mail.php
If that doesn't work then yes, your workaround will - call mail() twice. Fine except you don't really want to call it too much as automating that function can be construed as spam and you don't want that risk.