the headers already sent error means that there is output between php tags, see this post for details:
showthread.php?t=19285
the error is saying that the output is at line 6:
output started at /home/treebiz/public_html/Email.php:6
you probably have a blank space at the end of a php tag:
"?> "
or a blank line between the end of a php tag and the next opening tag:
?>
<?php