Estoy tratando de agregar la funcionalidad para enviar correos electrónicos a mis clientes desde el backend de mi sitio web y estoy tratando de usar swiftmailer para hacer esto. Lamentablemente sigo recibiendo un mensaje de error

Fatal error: Class 'Swift_smtpTransport' not found in /home/u312041955/public_html/cust/modules/customer/email.php on line 94

Aunque me parece que la clase swiftmailer no se incluye correctamente, debe ser así, de lo contrario, la página no muestra ninguna información. El código de la página desde la que estoy usando swiftmailer es el siguiente.

<?php require_once("include.php");
    //Required for swift mailer
    require_once (INCLUDE_URL.'/swift/lib/swift_required.php');
    if(!xml2php("customer")) {
    $smarty->assign('error_msg',"Error in language file");
    }
    // Lets grab some variables we need
    $email_username = $VAR['email_username'];
    $email_password = $VAR['email_password'];
    $email_server = $VAR['email_server2'];
    $email_server_port = $VAR['email_server_port2'];
    $customer_id = $VAR['customer_id'];
    $c2 = $VAR['c2'];
    $download_id = $VAR['download_id'];
    $submit = $VAR['submit'];
    $email_to = $VAR['email_to'];
    $email_from = $VAR['email_from'];
    $email_subject = $VAR['email_subject'];
    $message_body = $VAR['message_body'];
    $attachment = $VAR['attachment'];
    $rr_email = $VAR['rr'];
    $cus_name = $VAR['cus_name'];
    $sig = "<br>Regards,<br>".$employee_details ['EMPLOYEE_FIRST_NAME']."<br>MD-PC";

//Get All customer Emails
$q = "SELECT * FROM ".PRFX."TABLE_CUSTOMER_EMAILS WHERE CUSTOMER_ID ='".$customer_id."' ORDER BY CUSTOMER_EMAIL_ID DESC" ;
$rs = $db->Execute($q);
$customer_emails = $rs->GetArray();
$smarty->assign('customer_emails', $customer_emails);
/*Get Customer Info */
$q = "SELECT * FROM ".PRFX."TABLE_CUSTOMER WHERE CUSTOMER_ID ='".$customer_id."'" ;
$rs = $db->Execute($q);
$customer_details = $rs->GetArray();
$smarty->assign('customer_details', $customer_details);
/*Get Employee Info */
$q = "SELECT * FROM ".PRFX."TABLE_EMPLOYEE WHERE EMPLOYEE_DISPLAY_NAME ='".$login."'" ;
$rs = $db->Execute($q);
$employee_details = $rs->FetchRow();
$smarty->assign('employee_details', $employee_details);
// assign the arrays
$smarty->assign('open_work_orders', display_open_workorders($db, $customer_id));
$smarty->assign('closed_work_orders',   display_closed_workorders($db, $customer_id));
//$smarty->assign('customer_details',   display_customer_info($db, $customer_id));
$smarty->assign('customer_details',$customer_details);
$smarty->assign('unpaid_invoices', display_unpaid_invoices($db,$customer_id));
$smarty->assign('paid_invoices', display_paid_invoices($db,$customer_id));
$smarty->assign('memo', display_memo($db,$customer_id));
$smarty->assign('gift', display_gift($db, $customer_id));
$smarty->assign('company_details',display_company_info($db, $company_id));
//Lets Get the file downloaded to have a look at it from the database
if(isset ($download_id)){
 /*Get All customer Emails */
$q = "SELECT CUSTOMER_EMAIL_ATT_NAME1, CUSTOMER_EMAIL_ATT_TYPE1, CUSTOMER_EMAIL_ATT_SIZE1, CUSTOMER_EMAIL_ATT_FILE1,  FROM ".PRFX."TABLE_CUSTOMER_EMAILS WHERE CUSTOMER_EMAIL_ID ='".$download_id."'" ;
$rs = $db->Execute($q);
//header("Content-length: $rs->fields['CUSTOMER_EMAIL_ATT_SIZE1']");
//header("Content-type: $rs->fields['CUSTOMER_EMAIL_ATT_TYPE1']");
//header("Content-Disposition: attachment; filename=$rs->fields['CUSTOMER_EMAIL_ATT_NAME1']");
$file_download= $rs->fields['CUSTOMER_EMAIL_ATT_FILE1'];
$smarty->assign('file_download', $file_download);
//Print $CUSTOMER_EMAIL_ATT_NAME1;
 exit;

 }
// BOF Email Message details
//Mail
if(isset ($submit)){
    if($_FILES['attachment1']['size'] >  0 ){
    $fp      = fopen($_FILES['attachment1']['tmp_name'], 'r');
    $content1 = fread($fp, filesize($_FILES['attachment1']['tmp_name']));
    $content1 = addslashes($content1);
    fclose($fp);
    }
    $sql = "INSERT INTO ".PRFX."TABLE_CUSTOMER_EMAILS SET
            CUSTOMER_ID             = ". $db->qstr($VAR["c2"]).",
            CUSTOMER_EMAIL_ADDRESS  = ". $db->qstr( $VAR["email_to"]).",
            CUSTOMER_FROM_EMAIL_ADDRESS = ". $db->qstr( $VAR["email_from"]).",
            CUSTOMER_EMAIL_SENT_BY      = ". $db->qstr( $login ).", 
            CUSTOMER_EMAIL_SENT_ON      = ". $db->qstr( time()).",
            CUSTOMER_EMAIL_SUBJECT      = ". $db->qstr( $VAR["email_subject"]).",
            CUSTOMER_EMAIL_BODY = ". $db->qstr( $VAR["message_body"]).",
            CUSTOMER_EMAIL_ATT_NAME1    = ". $db->qstr( $_FILES['attachment1']['name']).",
            CUSTOMER_EMAIL_ATT_TYPE1        = ". $db->qstr( $_FILES['attachment1']['type']).",
            CUSTOMER_EMAIL_ATT_SIZE1        = ". $db->qstr( $_FILES['attachment1']['size']).",
            CUSTOMER_EMAIL_ATT_FILE1    = ". $db->qstr( $content1 ); 



    if(!$result = $db->Execute($sql)) {
        force_page('core', 'error&error_msg=MySQL Error: '.$db->ErrorMsg().'&menu=1&type=database');
        exit;
    }
//print $sql ;
    $transport = Swift_smtpTransport::newInstance( "mx1.hostinger.co.uk" , 2525 )
    ->setUsername('[email protected]')
    ->setPassword('******');
    $mailer = Swift_Mailer::newInstance($transport);
    //Create a message
    $message = Swift_Message::newInstance($email_subject)
      ->setFrom(array($email_from => $employee_details['EMPLOYEE_FIRST_NAME']))
     ->setTo(array($email_to => $cus_name))
     ->setBody($strip )
     ->addPart('Hello '.$cus_name , 'text/html')
     ->addPart($message_body, 'text/plain')
     ->attach(Swift_Attachment::fromPath($target_path));
     //Send the message
     $numSent = $mailer->send($message);
     //Display how many messages were sent
     echo "<script>alert('Email Information')</script>";
     echo "Sent %d messages\n", $numSent;
     exit(); 

    }
    ?>

He estado luchando con esto ahora o en algún momento y podría usar un empujón en la dirección correcta.

Actualización 1: he seguido jugando con esto y cuando cambio la línea

$transport = Swift_smtpTransport::newInstance( "mx1.hostinger.co.uk" , 2525 )
->setUsername('[email protected]')
->setPassword('******');

Simplemente

$transport = Swift_MailTransport::newInstance()

por lo que ya no usa SMTP, recibo un mensaje de notificación de envío exitoso, pero por alguna razón lo envía a la dirección de correo electrónico y también se marca como spam porque es posible que no se haya originado en la cuenta, por lo tanto, quiero usar smtp. Actualización 2: después de leer otros hilos encontré que

$transport = Swift_smtpTransport::newInstance( "mx1.hostinger.co.uk" , 2525 );

De hecho debería ser

$transport = Swift_SmtpTransport::newyInstance( "mx1.hostinger.co.uk" , 2525 )
;

Esto elimina el error de clase no encontrada, pero ahora recibo un error de tiempo de espera. Estoy seguro de que estoy usando los detalles correctos del servidor de correo cuando los obtuve de mi host. Cualquier ayuda muy apreciada.