jiliangzhifu2017/protected/class/swiftmailer/preferences.php

<?php

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/* YOU MAY WISH TO MODIFY OR REMOVE THE FOLLOWING LINES WHICH SET DEFAULTS  */
/*                                                                          */
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$preferences = Swift_Preferences::getInstance();

// Sets the default charset so that setCharset() is not needed elsewhere
$preferences->setCharset('utf-8');

// Without these lines the default caching mechanism is "array" but this uses a lot of memory.
// If possible, use a disk cache to enable attaching large attachments etc.
// You can override the default temporary directory by setting the TMPDIR environment variable.
if (@is_writable($tmpDir = sys_get_temp_dir())) {
    $preferences->setTempDir($tmpDir)->setCacheType('disk');
}

// this should only be done when Swiftmailer won't use the native QP content encoder
// see mime_deps.php
if (version_compare(phpversion(), '5.4.7', '<')) {
    $preferences->setQPDotEscape(false);
}