<?php
// autoloader here

$mail = new Zend_Mail('utf-8');
$mail->addTo('info@domain.de')
    ->setFrom('info@domain.de')
    ->setSubject('test 100m')
    ->setBodyText('test with 100mb attachment');
$mail->createAttachment(fopen("D:/temp/a.exe", "r"),
                        'application/octet-stream',
                        Zend_Mime::DISPOSITION_ATTACHMENT,
                        Zend_Mime::ENCODING_BASE64);


$config = array('auth' => 'login',
                'username' => 'XXXXX',
                'password' => 'XXXXXX');

$transport = new Zend_Mail_Transport_Smtp('smtp.domain.de', $config);

$mail->send($transport);

var_dump(memory_get_peak_usage());
var_dump(memory_get_peak_usage(true));