I would try, after making a copy of member.php:
find line 579
$body = "{$translate['textyourpwis']} \n\n{$translate['textusername']} $username\n{$translate['textpassword']} $password2\n\n$full_url";
xmb_mail( $rawemail, $subject, $body, $translate['charset'] );
} else {
replace with
$body = "{$translate['textyourpwis']} \n\n{$translate['textusername']} $username\n{$translate['textpassword']}
$password2\n\n$full_url";
xmb_mail( $rawemail, $subject, $body, $translate['charset'] );
} else if ($SETTINGS['approval'] == 'off') {