Try it this way

$smtp->data();
$smtp->datasend("To: $mailheaders{To}\n");
$smtp->datasend("From: $mailheaders{From}\n");
$smtp->datasend("Subject: $mailheaders{Subject}\n");
$smtp->datasend("Date: $smtpdate\n");
$smtp->datasend($message);
$smtp->dataend();
[download]

where $message contains text of the message